Flexible external gear, strain wave gear device, and robot device

Abstract

To provide a wave gear device which has large transmission torque while reducing a load exerted on external teeth when the external teeth engage with internal teeth.SOLUTION: A flexible external gear has: a flexible cylindrical barrel part; multiple external teeth; and a flange part. The flexible cylindrical barrel part extends in an axial direction with a center axis as its center. The multiple external teeth protrude from one axial end of the flexible cylindrical barrel part to the radial outer side. The flange part expands from the other axial end of the flexible cylindrical barrel part to the radial outer side. The flexible cylindrical barrel part has a cylindrical first barrel part and a cylindrical second barrel part. The first barrel part extends in the axial direction. The second barrel part is disposed at the other axial side relative to the first barrel part and extends in the axial direction. The external teeth protrude from a radial outer surface of the first barrel part to the radial outer side. On a cross section along the center axis, a radial inner surface of the first barrel part is disposed at the radial outer side relative to a radial inner surface of the second barrel part. The structure allows a wave motion generator having a larger diameter to be located at the radial inner side of the first barrel part.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Conventionally, a wave gear device including a rigid internal gear and a flexible external gear has been known. This type of wave gear device is mainly used as a reducer. A conventional wave gear device is disclosed, for example, in Japanese Patent Application Laid-Open No. 2000-055147. [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-055147 Summary of the Invention [Problem to be solved by the invention]

[0003] The top-hat type strain wave gearing (5) disclosed in JP 2000-055147 A includes an annular rigid internal gear, a flexible external gear (51), and an elliptical wave generator. The wave generator is fitted inside the flexible external gear (51). A portion of the flexible external gear (51) is disposed inside the rigid internal gear. The flexible external gear (51) also includes a cylindrical toothed portion (510), a cylindrical body portion (511), an annular diaphragm (512), and an annular boss (513) (see paragraph 0005, Figure 4, etc.). The cylindrical toothed portion (510) and the body portion (511) extend along a central axis (indicated by the dashed line in Figure 4). The cylindrical toothed portion (510) has external teeth (514) that are continuous with one end of the body portion (511). The diaphragm (512) extends radially outward from the edge of the other end opening of the body (511). The boss (513) is integrally formed on the outer periphery of the diaphragm (512). The width of the boss (513) along the central axis is greater than the width of the diaphragm (512) along the central axis.

[0004] The flexible external gear (51) is bent into an elliptical shape by the wave generator, and external teeth (514) formed at both ends of the elliptical shape in the major axis direction mesh with internal teeth formed on the inner circumferential surface of the rigid internal gear. When the wave generator is rotated by a motor shaft or the like, the meshing positions of the two gears move circumferentially. Relative rotation occurs between the two gears according to the difference in the number of teeth between the internal and external teeth (514). As shown in FIG. 4 of JP 2000-055147 A, the cylindrical toothed portion (510) and the body portion (511) extend along the central axis (indicated by the dashed line in FIG. 4). Therefore, by changing the shape of the flexible external gear including these portions, there is room for improvement, such as allowing a larger wave generator to be placed inside and reducing the overall weight of the flexible external gear.

[0005] An object of the present invention is to provide a technology that makes it possible to change the shape of a flexible external gear, place a larger wave generator on the inside, and reduce the weight of the entire flexible external gear. [Means for solving the problem]

[0006] The present invention is a flexible externally toothed gear having a cylindrical flexible cylindrical body portion extending in the axial direction centered on the central axis, a plurality of external teeth protruding radially outward from one axial end of the flexible cylindrical body portion, and a flange portion extending radially outward from the other axial end of the flexible cylindrical body portion, wherein the flexible cylindrical body portion has a cylindrical first body portion extending in the axial direction and a cylindrical second body portion extending in the axial direction and positioned on the other axial side of the first body portion, the external teeth protruding radially outward from the radially outer surface of the first body portion, and in a cross section along the central axis, the radially inner surface of the first body portion is positioned radially outward of the radially inner surface of the second body portion. [Effects of the Invention]

[0007] According to the present invention, in the flexible external gear, the radially inner surface of the first body portion, on whose radially outer surface the external teeth are formed, is positioned radially outward of the second body portion, which is positioned on the other axial side of the first body portion. This allows a wave generator with a larger diameter to be positioned radially inside the first body portion. As a result, a wave gearing device with a large transmission torque can be realized while reducing the load on the external teeth. Furthermore, by reducing the diameter of the second body portion, the weight of the entire flexible external gear, including the second body portion, can be reduced. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a vertical cross-sectional view of a strain wave gear device according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the strain wave gear device according to the first embodiment. [Figure 3] FIG. 3 is a partial vertical cross-sectional view of the flexible external gear according to the first embodiment. [Figure 4] FIG. 4 is a cross-sectional view of the flexible cylindrical body according to the first embodiment. [Figure 5] FIG. 5 is a vertical cross-sectional view of a strain wave gear device according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, exemplary embodiments of the present application will be described with reference to the drawings. In this application, the direction parallel to the central axis of a wave gearing device (described later) is referred to as the "axial direction," the direction perpendicular to the central axis of the wave gearing device is referred to as the "radial direction," and the direction along the arc centered on the central axis of the wave gearing device is referred to as the "circumferential direction." In addition, in this application, the axial direction is defined as the left-right direction, with the right side being defined as the "one axial side" and the left side being defined as the "other axial side," and the shape and positional relationship of each part will be described. However, this definition of the left-right direction is not intended to limit the orientation of the flexible external gear, wave gearing, and robot device according to the present invention when in use. In this application, the term "parallel direction" also includes a substantially parallel direction. In this application, the term "orthogonal direction" also includes a substantially orthogonal direction.

[0010] 1. First Embodiment The configuration of a wave gear device 100 according to a first embodiment of the present invention will be described below. Fig. 1 is a longitudinal cross-sectional view of the wave gear device 100 according to the first embodiment. Fig. 2 is a transverse cross-sectional view of the wave gear device 100 as viewed from the axial direction at position II in Fig. 1. Note that Fig. 2 schematically shows the shapes of the internal teeth 11 and external teeth 23, which will be described later.

[0011] The strain wave gearing 100 of this embodiment is a device that changes the speed of input rotational motion by utilizing the differential between a rigid internal gear 10 (described below) and a flexible external gear 20 (described below). The strain wave gearing 100 having the flexible external gear 20 of this embodiment is mounted to a joint of a robot device (not shown) and used as a reducer that decelerates and outputs rotational motion obtained from an electric motor. However, the strain wave gearing 100 of the present invention may also be incorporated into other devices such as an assist suit, a turntable, an indexing plate for a machine tool, a wheelchair, or an automated guided vehicle to realize various types of rotational motion.

[0012] As shown in Figures 1 and 2, the strain wave gearing 100 has a rigid internal gear 10, a first connecting portion 151, a second connecting portion 152, a flexible external gear 20, and a wave generator 30. The strain wave gearing 100 is also provided with an input portion (not shown) for obtaining power from an external source. The input portion is connected to, for example, a rotating portion of an electric motor, and extends cylindrically in the axial direction about a central axis 9. The input portion rotates about the central axis 9 together with the rotating portion of the electric motor.

[0013] The rigid internal gear 10 is a member that extends in an annular shape around the central axis 9. The rigid internal gear 10 has a rigidity that is much higher than that of a flexible cylindrical body 21, which will be described later. Therefore, the rigid internal gear 10 can be considered to be a substantially rigid body. As shown in FIG. 2 , a plurality of internal teeth 11 are formed on the inner peripheral surface of the rigid internal gear 10. The plurality of internal teeth 11 are arranged at a constant pitch along the circumferential direction. The rigid internal gear 10 also has a plurality of (eight in this embodiment) through holes 102. The plurality of through holes 102 are arranged at equal intervals in the circumferential direction around the central axis 9. Each through hole 102 also passes through the rigid internal gear 10 in the axial direction. The rigid internal gear 10 is fixed to the first connecting part 151 by screwing screws passing through each of the eight through holes 102 into screw holes 153 (described later) of the first connecting part 151 adjacent to the other axial side of the rigid internal gear 10. In addition, an output shaft (not shown) for extracting power after reduction is fixed to one axial side of the rigid internal gear 10.

[0014] The first connecting portion 151 is a member that extends cylindrically in the axial direction around the central axis 9. The second connecting portion 152 is disposed radially outward of the first connecting portion 151. The second connecting portion 152 has an inner diameter slightly larger than the outer diameter of the first connecting portion 151 and is a member that extends cylindrically in the axial direction around the central axis 9. Both the first connecting portion 151 and the second connecting portion 152 have high rigidity. The first connecting portion 151 is provided with a plurality of screw holes 153 for inserting screws that pass through the through holes 102 of the rigid internal gear 10. The second connecting portion 152 is provided with a plurality of through holes 154 for inserting screws (not shown) that are separately provided for connection to the flexible external gear 20. Each through hole 154 passes through the second connecting portion 152 in the axial direction.

[0015] The first connecting portion 151 is rotatably connected to the second connecting portion 152 by a bearing 16. A cross roller bearing is used as the bearing 16 in this embodiment. As shown in FIG. 1, the bearing 16 has a plurality of cylindrical rollers 1 between the inner peripheral surface of the second connecting portion 152 and the outer peripheral surface of the first connecting portion 151. 61The multiple cylindrical rollers 161 are arranged with their orientations alternating between an annular V-groove provided on the inner circumferential surface of the second connecting portion 152 and an annular V-groove provided on the outer circumferential surface of the first connecting portion 151. This allows the second connecting portion 152 and the first connecting portion 151 to be connected with high rigidity while allowing rotation of the first connecting portion 151 relative to the second connecting portion 152. Such cross roller bearings can obtain sufficient rigidity in the axial and radial directions without being used in pairs like ball bearings. In other words, using cross roller bearings can reduce the number of bearings provided in the strain wave gear device 100. This reduces the weight of the bearing 16 and also limits the axial dimension of the bearing 16.

[0016] FIG. 3 is a partial vertical cross-sectional view of the flexible external gear 20 according to the first embodiment. As shown in FIGS. 1 to 3, the flexible external gear 20 has a cylindrical flexible cylindrical body portion 21, an annular flange portion 22, and a plurality of external teeth 23. The flexible cylindrical body portion 21 is a portion extending in the axial direction about the central axis 9. The flexible cylindrical body portion 21 is also a cylindrical portion that is flexible and can bend in the radial direction. A plurality of external teeth 23 are formed on the radially outer surface of the flexible cylindrical body portion 21 (see the radially outer surface 71 in FIG. 3). Each of the plurality of external teeth 23 protrudes radially outward from a portion of the flexible cylindrical body portion 21, including an end portion on one axial side. As shown in FIG. 2, the plurality of external teeth 23 are arranged at a constant pitch along the circumferential direction.

[0017] The flange portion 22 is a portion that extends radially outward from the other axial end of the flexible cylindrical body portion 21. The flange portion 22 is a flat, annular portion that is less flexible than the flexible cylindrical body portion 21. A plurality of through holes 220 are provided in the radially outer portion of the flange portion 22. Each through hole 220 passes through the flange portion 22 in the axial direction. The flange portion 22 is axially fixed to the housing in which the strain wave gear device 100 is disposed by screwing the screws that pass through the through holes 154 of the second connecting portion 152 and the through holes 220 of the flange portion 22 into the housing.

[0018] The flexible cylindrical body 21 has a cylindrical first body 211, a cylindrical second body 212, and a connecting portion 213. The first body 211 extends axially on one axial side of the flexible cylindrical body 21. The first body 211 is located radially inside the rigid internal gear 10. The multiple external teeth 23 each protrude radially outward from a radially outer surface 71 of the first body 211. That is, the flexible external gear 20 has multiple external teeth 23 on the radially outer surface 71 of the first body 211. Furthermore, as will be described later, the external teeth 23 partially mesh with the multiple internal teeth 11 of the rigid internal gear 10 when the flexible cylindrical body 21 is pushed from the radially inside by the wave generator 30.

[0019] The second trunk portion 212 extends in the axial direction while being positioned on the other axial side of the first trunk portion 211. The connection portion 213 is located axially between the first trunk portion 211 and the second trunk portion 212, and expands radially outward as it moves toward one axial side. In this embodiment, the inclination angle θ of the connection portion 213 with respect to the central axis 9 is equal to or greater than 5 degrees and equal to or less than 30 degrees. However, it is sufficient that the inclination angle θ of the connection portion 213 with respect to the central axis 9 is approximately 45 degrees or less. By providing such a connection portion 213, the flexible external gear 20 can be made more flexible than when the first trunk portion 211 and the second trunk portion 212 are connected via a vertical step.

[0020] Furthermore, because the flexible external gear 20 has the above structure, in a cross section along the central axis 9 of the flexible external gear 20, the radially inner surface 72 of the first body portion 211 is positioned radially outward of the radially inner surface 73 of the second body portion 212. This allows the inner diameter of the first body portion 211 to be increased, and therefore allows a wave generator 30 with a larger diameter to be positioned radially inside the first body portion 211. As a result, when the external teeth 23 and the internal teeth 11 of the rigid internal gear 10 mesh, as described below, the load acting on the external teeth 23 can be reduced while the transmitted torque can be increased.

[0021] On the other hand, by reducing the diameter of the second body portion 212, it is possible to reduce the weight of the entire flexible external gear 20, including the second body portion 212. Furthermore, by having the flexible external gear 20 have a shape that is recessed in the radial direction near the second body portion 212, it is possible to provide a grease reservoir in the recessed location. In this case, as the flexible external gear 20 rotates about the central axis 9, the grease reaches the multiple external teeth 23 due to centrifugal force. As a result, it is possible to further reduce the load applied to the external teeth 23 when the external teeth 23 mesh with the internal teeth 11 of the rigid internal gear 10.

[0022] Furthermore, in this embodiment, in a cross section along the central axis 9 of the flexible external gear 20, the radially inner surface 72 of the first body portion 211 is disposed radially outward of the radially outer surface 74 of the second body portion 212. This allows the inner diameter of the first body portion 211 to be further increased, and therefore allows a wave generator 30 with an even larger diameter to be disposed radially inside the first body portion 211.

[0023] However, in a cross section along the central axis 9 of the flexible external gear 20, the radial position of the radially inner surface 72 of the first trunk portion 211 and the radial position of the radially outer surface 74 of the second trunk portion 212 may be approximately equal to each other. This makes it possible to prevent extreme deformation of the flexible external gear 20 while preventing the first trunk portion 211 and the second trunk portion 212 from being formed at extremely different radial positions.

[0024] Moreover, the second trunk portion 212 of this embodiment has an expanded diameter portion 214. At the end portion on the other axial direction in a cross section of the second trunk portion 212 along the central axis 9, the expanded diameter portion 214 expands radially outward in a curved shape as it approaches the other axial direction. The expanded diameter portion 214 is disposed axially opposite the end portion on the other axial direction of the radially outer surface 71 of the first trunk portion 211. In other words, the expanded diameter portion 214 overlaps with the radially outer surface 71 of the first trunk portion 211 on an axis parallel to the central axis 9. By structuring the flexible cylindrical trunk portion 21 in this way, the rigidity of the entire flexible external gear 20, including the expanded diameter portion 214, can be increased.

[0025] The flange portion 22 is connected to the other axially and radially outer end of the expanded diameter portion 214. The flange portion 22 has a constant axial width from the radially inner end connected to the expanded diameter portion 214 to the radially outer end. This allows the entire strain wave gear device 100, including the flange portion 22, to be made smaller in size in the axial direction.

[0026] In this embodiment, stainless steel is used as the material for the flexible external gear 20. However, the material for the flexible external gear 20 may also be steel with a relatively low carbon content, aluminum, or the like.

[0027] The flexible external gear 20 can be formed into its final shape by, for example, "pressing" a cylindrical member from a plate-shaped material, and then "squeezing" or "cutting." The external teeth 23 can be formed by rolling a roller against the cylindrical member. FIG. 4 is a cross-sectional view of the flexible cylindrical body 21 according to the first embodiment. When the external teeth 23 are formed by rolling a roller against the cylindrical member, as shown in FIG. 4, the radially inner surface 72 of the first body 211 has an uneven shape that follows the outer shape of the external teeth 23.

[0028] Furthermore, when the external teeth 23 are formed by pressing a roller against the above-mentioned cylindrical member and rolling the roller parallel to the central axis 9, the tooth traces 230 of the external teeth 23 are parallel to the central axis 9, as shown in Fig. 3. However, the roller may be pressed against the above-mentioned cylindrical member and rolled obliquely so that the tooth traces move radially outward as they move toward one axial side. In this case, the tooth traces of the radially outer portions of the external teeth 23 after molding are inclined radially outward as they move toward one axial side.

[0029] 1, a portion of the flexible cylindrical body 21, including one axial end, is disposed radially inside the rigid internal gear 10. The number of teeth of the internal teeth 11 of the rigid internal gear 10 is slightly different from the number of teeth of the external teeth 23 of the flexible external gear 20.

[0030] The wave generator 30 is a mechanism for flexibly deforming the flexible external gear 20. The wave generator 30 has a non-circular cam 31 and a flexible bearing 32. The wave generator 30 rotates around the central axis 9, as described below, radially inside the rigid internal gear 10 and the first body portion 211.

[0031] The non-circular cam 31 is a member that extends annularly about the central axis 9. The inner circumferential surface of the non-circular cam 31 is fixed to the outer circumferential surface of an input section that obtains power from outside the strain wave gearing 100, for example, using a key 103, which is a fixing member that extends in the axial direction, so that the two sections cannot rotate relative to each other. This allows the non-circular cam 31 to rotate together with the input section about the central axis 9 at the same rotation speed as before the speed reduction. However, the non-circular cam 31 may also be fixed to the input section using other methods, such as adhesive bonding or press fitting. The non-circular cam 31 of this embodiment has an elliptical cam profile. In other words, the non-circular cam 31 has an outer diameter that varies depending on the circumferential position.

[0032] The flexible bearing 32 is a flexible bearing located radially inward of the rigid internal gear 10 and the first barrel portion 211. The flexible bearing 32 has an inner ring 321, a plurality of balls 322, and an elastically deformable outer ring 323. The inner ring 321 is fixed to the outer peripheral surface of the non-circular cam 31. The plurality of balls 322 are interposed between the inner ring 321 and the outer ring 323 and arranged along the circumferential direction. The outer ring 323 elastically deforms (flexibly deforms) via the inner ring 321 and the balls 322 so as to reflect the cam profile of the rotating non-circular cam 31. The outer ring 323 also contacts the radially inner surface 72 of the first barrel portion 211. As described above, a ball bearing is used for the flexible bearing 32 in this embodiment. However, other types of bearings, such as roller bearings, may be used instead of ball bearings.

[0033] 1, in this embodiment, in a cross section along the central axis 9 of the flexible bearing 32, the outer peripheral surface 324 of the outer ring 323 is positioned slightly radially outward from the radially outer surface 74 of the second body portion 212 of the flexible cylindrical body 21. That is, in this embodiment, a flexible bearing 32 with a larger diameter can be used, and therefore the rotational torque required to deflect the flexible bearing 32 when the input part rotates can be reduced. As a result, input loss can be further reduced.

[0034] In the wave gear device 100 configured as described above, when the input section rotates at the rotational speed before reduction, the non-circular cam 31 and flexible bearing 32 of the wave generator 30 rotate together around the central axis 9. As described above, the wave generator 30 has an outer diameter that varies depending on the circumferential position. Therefore, as the wave generator 30 rotates around the central axis 9, the radially inner surface 72 of the first body portion 211 of the flexible cylindrical body 21 is pressed by the wave generator 30, causing the flexible cylindrical body 21 to bend radially and deform into an elliptical shape as seen in the axial direction, as shown in FIG. 2 . The external teeth 23 of the flexible external gear 20 mesh with the internal teeth 11 of the rigid internal gear 10 near the radially outer sides at two ends of the major axis of the ellipse formed by the non-circular cam 31. Near the two radially outer ends of the minor axis of the ellipse formed by the non-circular cam 31, the external teeth 23 of the flexible external gear 20 do not mesh with the internal teeth 11 of the rigid internal gear 10. In other words, in this embodiment, the external teeth 23 and the internal teeth 11 partially mesh with each other in the circumferential direction.

[0035] When the non-circular cam 31 rotates, the positions of both ends of the major axis of the ellipse formed by the non-circular cam 31 move in the circumferential direction, and therefore the meshing position between the external teeth 23 and the internal teeth 11 also moves in the circumferential direction. Here, as described above, the number of teeth of the internal teeth 11 of the rigid internal gear 10 is slightly different from the number of teeth of the external teeth 23 of the flexible external gear 20. Therefore, with each rotation of the non-circular cam 31, the meshing position between the internal teeth 11 and the external teeth 23 changes slightly. On the other hand, in this embodiment, the flexible external gear 20, together with the second connecting portion 152, is fixed to the housing in which the strain wave gearing 100 is disposed, and therefore does not rotate in the circumferential direction. As a result, the rigid internal gear 10, the first connecting portion 151, and the output shaft (not shown) rotate at a reduced rotational speed relative to the flexible external gear 20. In other words, the flexible external gear 20, the rigid internal gear 10 and the output shaft rotate relative to each other due to the difference in the number of teeth between the external teeth 23 and the internal teeth 11, while the radially inner surface 72 of the first body portion 211 of the flexible external gear 20 is pressed by the wave generator 30 and the meshing position between the external teeth 23 of the flexible external gear 20 and the internal teeth 11 of the rigid internal gear 10 moves circumferentially as the non-circular cam 31 rotates.

[0036] 2. Second Embodiment Next, the configuration of a wave gear device 100B according to a second embodiment of the present invention will be described. The following description will focus on differences from the first embodiment, and some overlapping descriptions of parts that are the same as those in the first embodiment will be omitted. Figure 5 is a vertical cross-sectional view of the wave gear device 100B according to the second embodiment.

[0037] 5, the strain wave gearing 100B includes a rigid internal gear 10B, a first connecting portion 151B, a second connecting portion 152B, a flexible external gear 20B, a wave generator 30B, a first support member 41B, a second support member 42B, a first support bearing 51B, and a second support bearing 52B. The strain wave gearing 100B also includes an input portion (not shown) for obtaining power from an external source. The rigid internal gear 10B, first connecting portion 151B, second connecting portion 152B, flexible external gear 20B, wave generator 30B, and input portion of this embodiment have the same configurations as the rigid internal gear 10, first connecting portion 151, second connecting portion 152, flexible external gear 20, wave generator 30, and input portion of the first embodiment, and therefore will not be described again.

[0038] The first support member 41B is a member that extends in the shape of an annular plate centered on the central axis 9B on one axial side of the rigid internal gear 10B and radially outside the non-circular cam 31B of the wave generator 30B. The first support member 41B is provided with a plurality of through holes 410B. Each through hole 410B passes through the first support member 41B in the axial direction. The rigid internal gear 10B is also provided with a plurality of through holes 102B. Each through hole 102B passes through the rigid internal gear 10B in the axial direction and is continuous with the through hole 410B of the first support member 41B. The first support member 41B and the rigid internal gear 10B are fixed to the first connecting portion 151B by screwing a screw 81B passing through the through hole 410B and the through hole 102B into a screw hole 153B of the first connecting portion 151B adjacent to the other axial side of the rigid internal gear 10B. In addition, an output shaft (not shown) for extracting power after reduction is fixed to one axial side of the first support member 41B.

[0039] The second support member 42B is a member that extends in the shape of an annular plate about the central axis 9B on the other axial side of the flange portion 22B of the flexible external gear 20B and radially outside the non-circular cam 31B of the wave generator 30B. A plurality of through holes 420B are formed in the second support member 42B. Each of the through holes 420B passes through the second support member 42B in the axial direction. Furthermore, a plurality of through holes 220B are formed in the flange portion 22B. Each of the through holes 220B passes through the flange portion 22B in the axial direction and is continuous with the through hole 420B of the second support member 42B. Furthermore, a plurality of through holes 154B are formed in the second connecting portion 152B adjacent to one axial side of the flange portion 22B. Each of the through holes 154B passes through the second connecting portion 152B in the axial direction and is continuous with the through hole 220B of the flange portion 22B. The second support member 42B, the flange portion 22B of the flexible external gear 20B, and the second connecting portion 152B are axially fixed to the housing in which the wave gear device 100B is disposed by screwing screws that pass through the through holes 420B, 220B, and 154B into the housing.

[0040] The first support bearing 51B is a bearing located radially inward of the first support member 41B and radially outward of the non-circular cam 31B. The first support bearing 51B has an inner ring 511B, multiple balls 512B, and an outer ring 513B. The inner ring 511B is fixed to the outer peripheral surface of the non-circular cam 31B. The multiple balls 512B are interposed between the inner ring 511B and the outer ring 513B and arranged along the circumferential direction. The outer ring 513B is fixed to the inner peripheral surface of the first support member 41B. This allows the first support member 41B, the rigid internal gear 10B, and the first connecting portion 151B to rotate relative to the wave generator 30B, which includes the non-circular cam 31B, about the central axis 9B. Furthermore, in this embodiment, by having the first support member 41B and the first support bearing 51B, the first support member 41B, the rigid internal gear 10B, and the first connecting portion 151B can be more stably supported for relative rotation with respect to the wave generator 30B including the non-circular cam 31B.

[0041] The second support bearing 52B is a bearing located radially inward of the second support member 42B and radially outward of the non-circular cam 31B. The second support bearing 52B has an inner ring 521B, a plurality of balls 522B, and an outer ring 523B. The inner ring 521B is fixed to the outer peripheral surface of the non-circular cam 31B. The plurality of balls 522B are interposed between the inner ring 521B and the outer ring 523B and arranged along the circumferential direction. The outer ring 523B is fixed to the inner peripheral surface of the second support member 42B. As a result, the wave generator 30B including the non-circular cam 31B is rotatably supported with respect to the second support member 42B, the flexible external gear 20B including the flange portion 22B, and the second connecting portion 152B. Furthermore, in this embodiment, by having the second support member 42B and the second support bearing 52B, the wave generator 30B including the non-circular cam 31B can be more stably rotatably supported relative to the second support member 42B, the flexible external gear 20B including the flange portion 22B, and the second connecting portion 152B.

[0042] In the strain wave gear device 100B configured as described above, when the input section rotates at the rotational speed before deceleration, the non-circular cam 31B and flexible bearing 32B of the wave generator 30B rotate together around the central axis 9B. The wave generator 30B has an outer diameter that varies depending on the circumferential position. Therefore, as the wave generator 30B rotates around the central axis 9B, the flexible cylindrical body portion 21B of the flexible external gear 20B is pushed from the radially inner side and bends radially, deforming into an elliptical shape when viewed in the axial direction. The external teeth 23B of the flexible external gear 20B mesh with the internal teeth 11B of the rigid internal gear 10B near two radially outer ends of the major axis of the ellipse formed by the non-circular cam 31B. Near the two radially outer ends of the minor axis of the ellipse formed by the non-circular cam 31B, the external teeth 23B of the flexible external gear 20B do not mesh with the internal teeth 11B of the rigid internal gear 10B. In other words, in this embodiment, the external teeth 23B and the internal teeth 11B partially mesh with each other in the circumferential direction.

[0043] When the non-circular cam 31B rotates, the positions of both ends of the major axis of the ellipse formed by the non-circular cam 31B move in the circumferential direction, and therefore the meshing position between the external teeth 23B and the internal teeth 11B also moves in the circumferential direction. Here, the number of teeth of the internal teeth 11B of the rigid internal gear 10B is slightly different from the number of teeth of the external teeth 23B of the flexible external gear 20B. Therefore, with each rotation of the non-circular cam 31B, the meshing position between the internal teeth 11B and the external teeth 23B changes slightly. On the other hand, in this embodiment, the flexible external gear 20B, together with the second connecting portion 152B and the second support member 42B, is fixed to the housing in which the strain wave gear device 100B is disposed, and therefore does not rotate in the circumferential direction. As a result, the rigid internal gear 10B, the first connecting portion 151B, the first support member 41B, and the output shaft (not shown) rotate at a reduced rotational speed relative to the flexible external gear 20B. In other words, the flexible external gear 20B, the rigid internal gear 10B, and the output shaft rotate relative to each other due to the difference in the number of teeth between the external teeth 23B and the internal teeth 11B, while the flexible cylindrical body portion 21B is pushed by the wave generator 30B and the non-circular cam 31B rotates, moving the meshing position between the external teeth 23B of the flexible external gear 20B and the internal teeth 11B of the rigid internal gear 10B in the circumferential direction.

[0044] <3. Modifications> Although the exemplary embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments.

[0045] In the first embodiment described above, the flexible external gear 20 and the second connecting portion 152 are fixed to a housing in which the strain wave gearing 100 is disposed and are configured not to rotate in the circumferential direction. However, instead of this configuration, the rigid internal gear 10 and the first connecting portion 151 may be fixed to a housing in which the strain wave gearing 100 is disposed and are not configured to rotate in the circumferential direction. An output shaft (not shown) for extracting power after reduction may then be fixed to the flange portion 22 of the flexible external gear 20.

[0046] In this case, too, when the non-circular cam 31 rotates, the positions of both ends of the major axis of the ellipse formed by the non-circular cam 31 move circumferentially, and therefore the meshing position between the external teeth 23 and the internal teeth 11 also moves circumferentially. Furthermore, the number of teeth of the internal teeth 11 of the rigid internal gear 10 is slightly different from the number of teeth of the external teeth 23 of the flexible external gear 20. Therefore, with each rotation of the non-circular cam 31, the meshing position between the internal teeth 11 and the external teeth 23 changes slightly. Meanwhile, the rigid internal gear 10 and the first connecting portion 151 are fixed to the housing in which the strain wave gearing 100 is disposed, and therefore do not rotate circumferentially. As a result, the flexible external gear 20, the second connecting portion 152, and the output shaft rotate at a reduced rotational speed relative to the rigid internal gear 10 and the first connecting portion 151. In other words, the flexible external gear 20, the second connecting portion 152, and the output shaft rotate relative to the rigid internal gear 10 due to the difference in the number of teeth between the external teeth 23 and the internal teeth 11, while moving the meshing position between the external teeth 23 of the flexible external gear 20 and the internal teeth 11 of the rigid internal gear 10 in the circumferential direction.

[0047] In the above embodiment, the flexible cylindrical body of the flexible external gear is provided with one connection portion that expands radially outward as it extends toward one axial side. However, the number of connection portions provided on the flexible cylindrical body may be two or more.

[0048] Furthermore, the detailed shapes of the flexible external gear, the strain wave gear device, and the robot device may differ from the shapes shown in the drawings of the above-described embodiment. [Industrial Applicability]

[0049] The present application can be used in flexible external gears, strain wave gear devices, and robotic devices. [Explanation of symbols]

[0050] 9,9B Center axis 10,10B Rigid internal gear 11,11B Internal teeth 16 Bearings 20,20B Flexible external gear 21, 21B Flexible cylindrical body 22, 22B flange 23,23B External teeth 30,30B Wave Generator 31,31B Non-circular cam 32,32B flexible bearing 71 (of the first body portion 211) radially outer surface 72 (of the first body portion 211) radially inner surface 73 (of the second body portion 212) radially inner surface 74 (of the second body portion 212) radially outer surface 100,100B Strain Wave Gearing 211 First body 212 Second body 213 Connection 214 Expanded diameter part 230 Tooth line 324 (of the outer ring 323 of the flexible bearing 32) outer surface θ (inclination angle of the connection part 213 relative to the central axis 9)

Claims

1. A flexible external gear, a flexible cylindrical body portion extending in an axial direction around a central axis; a plurality of external teeth protruding radially outward from one axial end of the flexible cylindrical body; a flange portion extending radially outward from the other axial end of the flexible cylindrical body portion; and The flexible cylindrical body portion includes: a cylindrical first body portion extending in an axial direction; a cylindrical second body portion that is disposed on the other axial side of the first body portion and extends in the axial direction; a connection portion located between the first body portion and the second body portion in the axial direction, the connection portion expanding radially outward as it extends toward one axial side; and the external teeth protrude radially outward from a radially outer surface of the first body portion, an inclination angle of the radially inner surface of the connection portion inclined radially outward with respect to the central axis as it moves toward one axial side is larger than an inclination angle of the radially inner surface of the first trunk portion inclined radially outward with respect to the central axis as it moves toward one axial side, and an inclination angle of the radially inner surface of the second trunk portion inclined radially outward with respect to the central axis as it moves toward one axial side, A flexible external gear, wherein in a cross section along the central axis, a radially inner surface of the first body portion is positioned radially outward of a radially inner surface of the second body portion.

2. 2. The flexible external gear according to claim 1, A flexible external gear, wherein in a cross section along the central axis, a radially inner surface of the first body portion is positioned radially outward of a radially outer surface of the second body portion.

3. 2. The flexible external gear according to claim 1, A flexible external gear, wherein, in a cross section taken along the central axis, the radial position of the radially inner surface of the first body portion and the radial position of the radially outer surface of the second body portion are equal to each other.

4. A flexible external gear according to any one of claims 1 to 3, the second body portion has an expanded diameter portion at an end portion on the other axial side in a cross section along the central axis, the expanded diameter portion expanding radially outward as it extends toward the other axial side, a flexible external gear, wherein a radially outer surface of the first body portion is disposed opposite the enlarged diameter portion in the axial direction.

5. 2. The flexible external gear according to claim 1, A flexible external gear, wherein the inclination angle of the connection portion with respect to the central axis is 45 degrees or less.

6. The flexible external gear according to claim 1 or claim 5, A flexible external gear, wherein the inclination angle of the connection portion with respect to the central axis is 30 degrees or less.

7. A flexible external gear according to any one of claims 1, 5, and 6, A flexible external gear, wherein the inclination angle of the connection portion with respect to the central axis is 5 degrees or more.

8. A flexible external gear according to any one of claims 1 to 7, A flexible external gear, wherein the tooth trace of the external teeth is parallel to the central axis.

9. A flexible external gear according to any one of claims 1 to 8, A flexible external gear, wherein the tooth trace of the radially outer portion of the external teeth is inclined radially outward as it moves toward one axial side.

10. A flexible external gear according to any one of claims 1 to 9, A flexible externally toothed gear, wherein a radially inner surface of the first body portion has an uneven shape that follows the outer shape of the external teeth.

11. A flexible external gear according to any one of claims 1 to 10, The flexible external gear is made of stainless steel, steel, or aluminum.

12. 5. The flexible external gear according to claim 4, A flexible external gear, wherein the flange portion has a constant axial width from the radially inner end connected to the expanded diameter portion to the radially outer end.

13. a rigid internal gear having a plurality of internal teeth on an inner peripheral surface thereof and extending in an annular shape around the central axis; a wave generator that rotates around the central axis on the radially inner side of the rigid internal gear and has an outer diameter that varies depending on the position in the circumferential direction; a flexible external gear according to any one of claims 1 to 12, having the external teeth partially meshing with the plurality of internal teeth of the rigid internal gear; and The wave generator comprises: a non-circular cam that rotates about the central axis and has an outer diameter that varies depending on a position in a circumferential direction; a flexible bearing having an inner ring to which the non-circular cam is fixed and an outer ring to which the flexible external gear is brought into contact; and The flexible external gear and the rigid internal gear rotate relative to each other due to the difference in the number of teeth between the internal teeth and the external teeth, while the radially inner surface of the first body portion of the flexible external gear is pressed by the wave generator and the meshing position between the internal teeth and the external teeth moves circumferentially as the non-circular cam rotates.

14. 14. The strain wave gear device according to claim 13, In a cross section taken along the central axis, an outer peripheral surface of the outer ring of the flexible bearing is positioned radially outward of a radially outer surface of the second body portion.

15. A robot device equipped with the flexible external gear according to any one of claims 1 to 12.

16. A robot device equipped with the strain wave gear device according to claim 13 or 14.

Images