Wave gear device and actuator

Abstract

To provide a wave gear device and an actuator hard to be degraded in reliability.SOLUTION: A wave gear device 1 includes a rigid internal gear 2, a flexible external gear 3, and a wave motion 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 disposed inside of the rigid internal gear 2. The wave motion generator 4 is disposed inside of the flexible external gear 3, and generates deflection on the flexible external gear 3. In the wave gear device 1, the flexible external gear 3 is deformed in accompany with rotation of the wave motion generator 4 on a rotating axis Ax1 as a center, a part of the external teeth 31 is engaged with a part of the internal teeth 21, and the flexible external gear 3 is relatively rotated to the rigid internal gear 2 according to difference in number of teeth with respect to the rigid internal gear 2. Surface hardness of the internal teeth 21 is lower than surface hardness of the external teeth 31. The external teeth 31 project to at least one side in a tooth muscle direction D1, with respect to the internal teeth 21.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present disclosure relates generally to strain wave gearing and actuators, and more particularly to strain wave gearing and actuators including a rigid internal gear, a flexible external gear, and a strain wave generator. [Background technology]

[0002] Patent Document 1 discloses that the surface of a flexible external gear in a strain wave gear device (flexible mesh gear device) is treated by nitriding.

[0003] The wave gear device has an annular rigid internal gear, a cup-shaped flexible external gear placed inside the rigid internal gear, and an elliptical wave generator fitted inside the flexible external gear. The flexible external gear has a cylindrical body and external teeth formed on the outer peripheral surface of the body. The flexible external gear is bent into an elliptical shape by the wave generator, and the external teeth located at both ends of the elliptical shape in the major axis direction mesh with internal teeth formed on the inner peripheral surface of the rigid internal gear.

[0004] When the wave generator is rotated by a motor or the like, the meshing positions of the two gears move circumferentially, and a relative rotation occurs between the two gears according to the difference in the number of teeth between the internal and external gears (2N (N is a positive integer)). Here, when the rigid internal gear is fixed, a rotational output is obtained from the flexible external gear that is significantly reduced in speed according to the difference in the number of teeth between the two gears. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-59153 Summary of the Invention [Problem to be solved by the invention]

[0006] However, because a strain wave gearing transmits power by meshing the internal and external teeth while flexing the flexible external gear, foreign matter such as metal powder or nitrides can be generated, particularly over long periods of use, due to chipping or wear caused by contact between the internal and external teeth. The generation of such foreign matter can lead to foreign matter getting caught between the internal and external teeth or to foreign matter getting into the bearings of the wave generator, damaging the bearings and potentially affecting the reliability of the strain wave gearing.

[0007] The present disclosure has been made in view of the above circumstances, and has an object to provide a strain wave gear device and an actuator that are less likely to experience a decrease in reliability. [Means for solving the problem]

[0008] 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 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 in response to rotation of the wave generator about a rotation axis, meshing some of the external teeth with some 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 rigid internal gear and the flexible external gear. The surface hardness of the internal teeth is lower than that of the external teeth. The external teeth protrude in at least one tooth trace direction relative to the internal teeth.

[0009] An actuator according to one aspect of the present disclosure includes the strain wave gearing, a drive source, and an output unit. The drive source rotates the wave generator. The output unit extracts the rotational force of either the rigid internal gear or the flexible external gear as an output. [Effects of the Invention]

[0010] The present disclosure has the advantage of being able to provide a strain wave gear device and an actuator that are less likely to experience a decrease in reliability. [Brief explanation of the drawings]

[0011] [Figure 1A] FIG. 1A is a cross-sectional view showing a schematic configuration of a strain wave gear device according to a first embodiment. [Figure 1B] FIG. 1B is an enlarged view of region Z1 of FIG. 1A. [Figure 2] FIG. 2 is a schematic diagram of the strain wave gear device as viewed from the input side of the rotary shaft. [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 5A] FIG. 5A is a schematic cross-sectional view of the above strain wave gear device, focusing on the internal teeth and external teeth. [Figure 5B] FIG. 5B is a cross-sectional view taken along line A1-A1 in FIG. 5A. [Figure 6] FIG. 6 is a conceptual explanatory diagram showing the amount of modification of the internal teeth and external teeth of the strain wave gear device. [Figure 7A] FIG. 7A is a cross-sectional view taken along line B1-B1 in FIG. 5A. [Figure 7B] FIG. 7B is a cross-sectional view taken along line B2-B2 in FIG. 5A. [Figure 7C] FIG. 7C is a cross-sectional view taken along line B3-B3 in FIG. 5A. [Figure 8A] FIG. 8A is a schematic cross-sectional view of the periphery of the inner peripheral surface of a flexible external gear of the strain wave gear device. [Figure 8B] FIG. 8B is an enlarged view of region Z1 in FIG. 8A. [Figure 9] FIG. 9 is a cross-sectional view showing an example of a robot using the above strain wave gear device. [Figure 10A]FIG. 10A is a cross-sectional view of a main part of a wave gear device according to a first modified example of the first embodiment. [Figure 10B] FIG. 10B is a cross-sectional view of a main part of a wave gear device according to a second modified example of the first embodiment. [Figure 10C] FIG. 10C is a cross-sectional view of a main part of a strain wave gear device according to a third modified example of the first embodiment. [Figure 10D] FIG. 10D is a cross-sectional view of a main part of a wave gear device according to a fourth modified example of the first embodiment. [Figure 11A] FIG. 11A is a schematic cross-sectional view focusing on the internal teeth and external teeth of a strain wave gear device according to a second embodiment. [Figure 11B] FIG. 11B is a cross-sectional view taken along line A1-A1 in FIG. 11A. [Figure 12A] FIG. 12A is a cross-sectional view taken along line B1-B1 in FIG. 11A. [Figure 12B] FIG. 12B is a cross-sectional view taken along line B2-B2 in FIG. 11A. [Figure 12C] FIG. 12C is a cross-sectional view taken along line B3-B3 in FIG. 11A. [Figure 13] FIG. 13 is a schematic cross-sectional view focusing on the internal teeth and external teeth of a strain wave gear device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Embodiment 1) (1) Overview An overview of the wave gear device 1 according to this embodiment 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 2 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 embodiment is a gearing including 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 wave gearing 1, the wave generator 4 having the bearing 42 flexes the flexible external gear 3, and power is transmitted by the meshing of the internal teeth 21 and the external teeth 31. Therefore, particularly with long-term use, for example, contact between the internal teeth 21 and the external teeth 31 can cause chipping or wear, resulting in the generation of foreign matter X1 (see FIG. 8B ), such as metal powder or nitride. The generation of such foreign matter X1 can lead to the foreign matter X1 becoming caught between the internal teeth 21 and the external teeth 31, or to the foreign matter X1 entering the bearing 42 of the wave generator 4, damaging the bearing 42 and potentially affecting the reliability of the wave gearing 1. For example, if the foreign matter X1 enters the bearing 42, an indentation caused by the foreign matter X1 getting caught between the outer ring 421 or inner ring 422 and the rolling element 423 of the bearing 42 can be generated, and damage can occur on the surface of any of the outer ring 421, inner ring 422, and rolling element 423. This type of damage (surface-originating flaking) leads to deterioration in the quality and characteristics of the strain wave gearing 1, which ultimately leads to a decrease in the reliability of the strain wave gearing 1. The strain wave gearing 1 according to this embodiment is configured as follows to make it less likely for foreign matter X1 to be generated, thereby making it less likely for a decrease in reliability to occur.

[0016] 1A to 3B, the wave gearing 1 according to this embodiment includes an annular rigid internal gear 2 having internal teeth 21, an annular flexible external gear 3 having external teeth 31, and a wave generator 4. The flexible external gear 3 is disposed inside the rigid internal gear 2. The wave generator 4 is disposed inside the flexible external gear 3 and causes deflection in the flexible external gear 3. The wave gearing 1 deforms the flexible external gear 3 as the wave generator 4 rotates 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 relative to the rigid internal gear 2 in accordance with the difference in the number of teeth between the rigid internal gear 2 and the flexible external gear 3. Here, the internal teeth 21 have a tooth trace modification portion 210 at least on one end of the internal teeth 21 in the tooth trace direction D1.

[0017] According to this aspect, the internal teeth 21 have tooth trace modification portions 210 at least on one end of the internal teeth 21 in the tooth trace direction D1. The tooth trace modification portions 210 of the internal teeth 21 form a "relief" between them and the external teeth 31, and therefore the tooth trace modification portions 210 can prevent stress concentration due to excessive tooth contact with the external teeth 31 at least on one end of the internal teeth 21 in the tooth trace direction D1. In particular, in the strain wave gearing 1, when the wave generator 4 flexes the flexible external gear 3, deformations such as twisting and tilt (inclination) of the external teeth 31 with respect to the rotation axis Ax1 can occur. Therefore, stress concentration due to deformation of the external teeth 31 is likely to occur at least on one end of the internal teeth 21 in the tooth trace direction D1, but the tooth trace modification portions 210 can prevent such stress concentration from occurring. This makes it possible to provide a strain wave gearing 1 that is less susceptible to the generation of foreign matter X1 due to chipping or wear caused by contact between the internal teeth 21 and the external teeth 31, and is less susceptible to a decrease in reliability. Furthermore, by providing the tooth trace modification portion 210 on the rigid internal gear 2, tooth trace modification for the flexible external gear 3 is unnecessary or the amount of modification can be reduced, making it easier to prevent a decrease in strength of the flexible external gear 3 that would be caused by applying tooth trace modification to the flexible external gear 3.

[0018] Furthermore, in the wave gear device 1 according to this embodiment, the surface hardness of the internal teeth 21 is lower than the surface hardness of the external teeth 31. The external teeth 31 protrude relative to the internal teeth 21 in at least one direction in the tooth trace direction D1.

[0019] According to this embodiment, the external teeth 31, which have a relatively high surface hardness, protrude in at least one direction in the tooth trace direction D1 compared to the internal teeth 21, and therefore steps due to wear are unlikely to occur on the tooth surfaces of the internal teeth 21 in at least one direction in the tooth trace direction D1. In other words, in at least one direction in the tooth trace direction D1, the internal teeth 21, which have a relatively low surface hardness, are uniformly worn by contact with the external teeth 31, and therefore localized depressions (steps) are unlikely to occur on the tooth surfaces of the internal teeth 21. Therefore, even if the tooth contact position shifts in the tooth trace direction D1 due to some kind of accident, it is easy to prevent abnormalities in the strain wave gear device 1 caused by excessive load being applied to the meshing portion between the internal teeth 21 and the external teeth 31. In other words, chipping is unlikely to occur in corner portions such as one end of the external teeth 31 in the tooth trace direction D1, and as a result, hard (relatively hard) foreign matter X1 is unlikely to occur. Therefore, foreign matter X1 is less likely to be generated due to chipping or wear caused by contact between the internal teeth 21 and the external teeth 31, making it possible to provide a strain wave gear device 1 that is less likely to experience a decrease in reliability.

[0020] In short, the wave gear device 1 according to this embodiment has the effect of making it less likely for the foreign matter X1 to be generated, thereby making it less likely for reliability to decline. Furthermore, the wave gear device 1 according to this embodiment is less likely to experience a decline in reliability, especially during long-term use, which in turn leads to a longer life and higher performance of the wave gear device 1.

[0021] 4, the wave gearing 1 according to this embodiment, together with a drive source 101 and an output unit 102, constitutes an actuator 100. In other words, the actuator 100 according to this embodiment 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.

[0022] The actuator 100 according to this embodiment has the advantage that the reliability of the strain wave gear device 1 is less likely to decrease.

[0023] (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.

[0024] In this disclosure, "tooth trace modification" refers to modification in the tooth trace direction D1, and the tooth trace modification portion 210 of the internal tooth 21 is the portion of the internal tooth 21 where the tooth trace modification has been applied. Tooth trace modification can intentionally add a bulge to the normal tooth trace shape of a gear or change the helix angle. Typical tooth trace modification processes include crowning and relieving (end relief). Crowning is a process that rounds the center of the gear in the tooth trace direction D1 so that the center is convex in the tooth trace direction D1. Relieving is a process that appropriately relieves both ends of the tooth in the tooth trace direction D1. While crowning is a process that rounds the center over approximately the entire length of the tooth in the tooth trace direction D1, relieving is a process that only relieves both ends of the tooth in the tooth trace direction D1. In either crowning or relieving, by making the tooth thickness at both ends in the tooth trace direction D1 smaller than at the center, the tooth contact position with the mating gear can be moved closer to the center in the tooth trace direction D1. This type of tooth trace modification prevents "uneven contact" in which tooth contact is biased to one end in the tooth trace direction D1 due to gear manufacturing or assembly errors, and alleviates stress concentration particularly at the ends in the tooth trace direction D1 (face width ends), improving tooth contact.

[0025] In this disclosure, "foreign matter" refers to a substance other than the original components of the wave gear device 1, and examples include metal powder or nitrides that are generated due to chipping or wear caused by contact between the internal teeth 21 and the external teeth 31. Furthermore, the foreign matter X1 whose entry is hindered by the lubricant Lb1 (see FIG. 8B) described below is not limited to substances generated inside the wave gear device 1, but also includes, for example, dirt, sand, dust, or other particles that enter from outside the wave gear device 1. "Hindering" here means to obstruct or impede, and is not limited to completely blocking, but generally includes making it difficult for the foreign matter X1 to enter.

[0026] In this disclosure, "reducing the generation of foreign matter X1" means reducing at least one of the generation amount, generation rate, and generation frequency of foreign matter X1 (hereinafter referred to as "generation amount, etc."). Here, the generation amount, etc. refers to values ​​particularly for foreign matter X1 of hardness and size that could cause a decrease in the reliability of the strain wave gearing 1. Reducing the generation of foreign matter X1 includes, for example, a reduction in the generation amount of hard (relatively hard) foreign matter X1. Of course, completely eliminating the generation of foreign matter X1 also includes reducing the generation amount of foreign matter X1. In other words, in this embodiment, by adopting a configuration in which the tooth trace modification portion 210 is provided at at least one end of the internal tooth 21 in the tooth trace direction D1, the generation amount of foreign matter X1 is reduced compared to when this configuration is not adopted. Similarly, in this embodiment, by adopting a configuration in which the external tooth 31, which has a relatively high surface hardness, protrudes from the internal tooth 21 in at least one side in the tooth trace direction D1, the generation amount of foreign matter X1 is reduced compared to when this configuration is not adopted.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] In the present 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 embodiment, as an example, the non-circular cam 41 of the wave generator 4 is elliptical. In other words, in this embodiment, the wave generator 4 bends the flexible external gear 3 into an elliptical shape.

[0031] In this disclosure, the term "elliptical shape" refers to a general 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 embodiment 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. 2, 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.

[0032] 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 with no physical substance. The wave generator 4 performs rotational motion around the axis of rotation Ax1.

[0033] 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 of the flexible external gear 3.

[0034] 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.

[0035] (3) Composition The detailed configurations of the strain wave gear device 1 and the actuator 100 according to this embodiment will be described below with reference to FIGS. 1A to 6C.

[0036] Fig. 1A is a cross-sectional view showing the schematic configuration of the strain wave gearing 1, and Fig. 1B is an enlarged view of area Z1 in Fig. 1A. Fig. 2 is a schematic view of the strain wave gearing 1 as viewed from the input side of the rotational axis Ax1 (right side of Fig. 1A). Fig. 3A is a schematic exploded perspective view of the strain wave gearing 1 as viewed from the output side of the rotational axis Ax1 (left side of Fig. 1A). Fig. 3B is a schematic exploded perspective view of the strain wave gearing 1 as viewed from the input side of the rotational axis Ax1. Fig. 4 is a cross-sectional view showing the schematic configuration of an actuator 100 including the strain wave gearing 1.

[0037] (3.1) Strain wave gearing As described above, the wave gearing 1 according to this embodiment includes the rigid internal gear 2, the flexible external gear 3, and the wave generator 4. In this embodiment, the materials of the rigid internal gear 2, the flexible external gear 3, and the wave generator 4, which are components of the 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 metals referred to here include metals that have been subjected to surface treatments such as nitriding.

[0038] In addition, in this embodiment, 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 embodiment 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 inside the cup-shaped flexible external gear 3.

[0039] In addition, in this embodiment, as an example, the strain 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.).

[0040] Furthermore, in this embodiment, when the 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 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 wave gearing 1 produces output rotation that is reduced at a relatively high reduction ratio relative to the input rotation.

[0041] Furthermore, in the wave gear device 1 according to this embodiment, 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 gear device 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.

[0042] The rigid internal gear 2 is also called a circular spline, and is an annular component having internal teeth 21. In this embodiment, 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 constituting 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 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.

[0043] 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.

[0044] The flexible external gear 3, also known as a flex spline, is an annular component having external teeth 31. In this embodiment, the flexible external gear 3 is a component formed into a cup shape using 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 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 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 that is 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, having 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 embodiment, the trunk 321 and the bottom 322 are integrally formed from a single metal member, thereby realizing a seamless main body 32.

[0045] 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 receives 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 embodiment, 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.

[0046] 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 assumes a shape closer to an ellipse. 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 302 (see FIG. 8A ) that is inclined with respect to the rotation axis Ax1.

[0047] Furthermore, the external teeth 31 are formed along the circumferential direction of the body portion 321, at least on the end of the outer circumferential surface 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 at least on the end of the body portion 321 of the flexible external gear 3 that is on the opening surface 35 side in the direction of the rotation axis Ax1. The multiple teeth that make up the external teeth 31 all have the same shape and are provided at an equal pitch over the entire circumferential area of ​​the outer circumferential surface 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, external teeth 31 are formed on the outer circumferential surface of 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). The tooth traces of the external teeth 31 are all parallel to the rotation axis Ax1.

[0048] In short, in the wave gear device 1 according to this embodiment, 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 embodiment, 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.

[0049] In this embodiment, 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.

[0050] The flexible external gear 3 configured in this manner is disposed inside the rigid internal gear 2. The flexible external gear 3 is combined with the rigid internal gear 2 so that only the end of the outer circumferential surface of the body 321 opposite the bottom 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 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. External teeth 31 are formed on the outer circumferential surface 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.

[0051] 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 embodiment, 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.

[0052] 1A and 1B, as an example, in this embodiment, 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 at the same position in the direction of the rotation axis Ax1. In addition, in this embodiment, 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. Details will be explained in the section "(4.3) Tooth Width," but in this embodiment, the external teeth 31 protrude relative to the internal teeth 21 on both sides of the tooth trace direction D1 (on the input and output sides of the rotation axis Ax1).

[0053] 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.

[0054] 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. 2. 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.

[0055] The wave generator 4 is also called a wave generator, and is a component that causes deflection in the flexible external gear 3 to generate wave motion in the external teeth 31 of the flexible external gear 3. In this embodiment, the wave generator 4 is a component whose outer circumferential shape is non-circular, specifically elliptical, in plan view.

[0056] 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.

[0057] 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 approximately the same 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 embodiment, as described above, the rotation of the wave generator 4 is defined as 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.

[0058] The bearing 42 has an outer ring 421, an inner ring 422, and a plurality of rolling elements 423. In this embodiment, as an example, the bearing 42 is a deep groove ball bearing using balls as the rolling elements 423.

[0059] 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 embodiment, the outer ring 421 and the inner ring 422 each have an annular shape that is a perfect circle in a plan view when no elastic deformation occurs in the bearing 42 (when the cam 41 is not combined with the bearing 42). The inner ring 422 is one size 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 of the outer ring 421 and the outer peripheral surface of the inner ring 422.

[0060] 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.

[0061] In the present embodiment, as an example, the dimensions of the outer ring 421 and the inner ring 422 in the width direction (the 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.

[0062] 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.

[0063] 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.

[0064] The wave generator 4 configured in this manner 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 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.

[0065] In the strain wave gearing 1 configured as described above, as shown in Fig. 2, 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.

[0066] As a result, wave motion is generated in the external teeth 31 formed on the outer peripheral surface 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, 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 position between the internal teeth 21 and the external teeth 31 moves. In this way, the wave gear device 1 according to this embodiment 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.

[0067] 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.

[0068] 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).

[0069] According to the strain wave gear device 1 of this embodiment, such a high reduction ratio R1 can be achieved with a combination of one gear stage (rigid internal gear 2 and flexible external gear 3).

[0070] 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."

[0071] (3.2) Actuator Next, the configuration of the actuator 100 according to this embodiment will be described in more detail.

[0072] As shown in Fig. 4, the actuator 100 according to this embodiment includes the strain wave gearing 1 according to this embodiment, 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 strain wave gearing 1. In addition to the strain wave gearing 1, the drive source 101, and the 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 embodiment, 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.

[0073] In this embodiment, 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.

[0074] 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.

[0075] 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.

[0076] 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 embodiment, 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.

[0077] The input side case 111 holds the input part 103 via input side bearings 118 and 119 so that the input part 103 is rotatable. 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 embodiment, a 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.

[0078] The output side case 112 holds the output part 102 via output side bearings 121 and 122 so that the output part 102 is rotatable. 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 embodiment, 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] (4) Configuration of inner and outer teeth Next, the configuration of the internal teeth 21 and external teeth 31 of the wave gear device 1 according to this embodiment will be described in more detail with reference to FIGS. 5A to 8B.

[0084] FIG. 5A is a cross-sectional view focusing on the internal teeth 21 and external teeth 31 in FIG. 1B, and FIG. 5B is a cross-sectional view taken along line A1-A1 in FIG. 5A. FIG. 6 is a conceptual explanatory diagram showing the adjustment amounts Q1 and Q2 of the internal teeth 21 and external teeth 31, illustrating a state in which the internal teeth 21 and external teeth 31 are disengaged from the state shown in FIG. 5A. FIG. 7A is a cross-sectional view taken along line B1-B1 in FIG. 5A, FIG. 7B is a cross-sectional view taken along line B2-B2 in FIG. 5A, and FIG. 7C is a cross-sectional view taken along line B3-B3 in FIG. 5A. FIG. 8A is a cross-sectional view showing a tapered surface 302 inclined with respect to the rotation axis Ax1 on the inner peripheral surface 301 of the flexible external gear 3, and FIG. 8B is an enlarged view of region Z1 in FIG. 8A. As mentioned above, all drawings referred to in this disclosure are schematic views, and the ratios of the sizes and thicknesses of the components in the drawings do not necessarily reflect the actual dimensional ratios. 5A to 7C, the modification amounts Q1 and Q2 of the tooth lead modification are exaggerated, and are not intended to limit the actual shapes of the internal teeth 21 and external teeth 31. Furthermore, hatching (diagonal lines) of cross sections is omitted in FIGS.

[0085] (4.1) Surface hardness First, the surface hardness of the internal teeth 21 and the external teeth 31 in this embodiment will be described.

[0086] In this embodiment, as described above, the surface hardness of the internal teeth 21 is lower than that of the external teeth 31. In other words, the surface of the external teeth 31 is harder than the surface of the internal teeth 21. In this disclosure, "hardness" refers to the degree of hardness of an object, and the hardness of a metal is expressed, for example, by the size of an indentation made when a steel ball is pressed against it with a certain pressure. Specifically, examples of metal hardness include Rockwell hardness (HRC), Brinell hardness (HB), Vickers hardness (HV), and Shore hardness (Hs). In this embodiment, hardness is expressed by Vickers hardness (HV) unless otherwise specified. Methods for increasing the hardness of a metal part include, for example, alloying or heat treatment.

[0087] In this embodiment, the surfaces of the external teeth 31 of the flexible external gear 3 are made of a material that is high in hardness and toughness (strength), while the internal teeth 21 of the rigid internal gear 2 are made of a material that is lower in hardness than the external teeth 31. In this embodiment, as an example, the external teeth 31 are made of a material that is a heat-treated (quenched and tempered) nickel-chromium-molybdenum steel specified as "SNCM439" in the Japanese Industrial Standards (JIS). The internal teeth 21 are made of spheroidal graphite cast iron specified as "FCD800-2" in the Japanese Industrial Standards (JIS).

[0088] Furthermore, the surface hardness of the internal teeth 21, which are relatively lower than the external teeth 31, is preferably HV350 or less. In this embodiment, as an example, the surface hardness of the internal teeth 21 is selected from the range of HV250 or more to less than HV350. The lower limit of the surface hardness of the internal teeth 21 is not limited to HV250 and may be, for example, HV150, HV160, HV170, HV180, HV190, HV200, HV210, HV220, HV230, or HV240. Similarly, the upper limit of the surface hardness of the internal teeth 21 is not limited to HV350 and may be, for example, HV360, HV370, HV380, HV390, HV400, HV410, HV420, HV430, HV440, or HV450.

[0089] In contrast, the surface hardness of the external teeth 31, which are relatively hard compared to the internal teeth 21, is preferably HV380 or higher. In this embodiment, as an example, the surface hardness of the external teeth 31 is selected from the range of HV380 or higher to HV450 or lower. The lower limit of the surface hardness of the external teeth 31 is not limited to HV380 and may be, for example, HV280, HV290, HV300, HV310, HV320, HV330, HV340, HV350, HV360, or HV370. Similarly, the upper limit of the surface hardness of the internal teeth 21 is not limited to HV450 and may be, for example, HV460, HV470, HV480, HV490, HV500, HV510, HV520, HV530, HV540, or HV550.

[0090] In this embodiment, the difference in surface hardness between the internal teeth 21 and the external teeth 31 is HV50 or more. In other words, the surface hardness of the external teeth 31 is set to be HV50 or more higher than the surface hardness of the internal teeth 21. In other words, if the surface hardness of the internal teeth 21 is HV350, for example, the surface hardness of the external teeth 31 is HV400 or more. Furthermore, if the surface hardness of the external teeth 31 is HV380, the surface hardness of the internal teeth 21 is HV330 or less. The difference in surface hardness between the internal teeth 21 and the external teeth 31 is not limited to HV50 or more, and may be, for example, HV20 or more, HV30 or more, or HV40 or more. Furthermore, a larger difference in surface hardness between the internal teeth 21 and the external teeth 31 is preferable, and more preferably, for example, HV60 or more, HV70 or more, HV80 or more, HV90 or more, or HV100 or more. If the difference between the surface hardness of the internal teeth 21 and the surface hardness of the external teeth 31 is HV100 or more, when the surface hardness of the internal teeth 21 is HV350, the surface hardness of the external teeth 31 is HV450 or more.

[0091] As described above, in this embodiment, the surface hardness of the internal teeth 21 is set lower than that of the external teeth 31. Therefore, when the internal teeth 21 and the external teeth 31 come into contact during operation of the wave gearing 1, the internal teeth 21, which have a relatively low surface hardness, wear more aggressively than the external teeth 31. When two components (the internal teeth 21 and the external teeth 31) with different surface hardnesses come into contact, the wear of the relatively soft internal teeth 21 progresses, thereby suppressing the wear of the relatively hard external teeth 31. In other words, in the early stages of use of the wave gearing 1, the tooth surfaces of the internal teeth 21 wear moderately, which increases the true contact area between the internal teeth 21 and the external teeth 31 and reduces the surface pressure, making it difficult for the external teeth 31 to wear. Furthermore, when the surface hardness of the internal teeth 21 is HV350 or less as in this embodiment, even if foreign matter X1 is generated due to chipping or wear of the internal teeth 21 caused by contact between the internal teeth 21 and the external teeth 31, this foreign matter X1 is relatively soft. In short, by making the foreign matter X1 that is likely to be generated due to wear in the early stages of use of the wave gear device 1 into soft foreign matter X1 that comes out from the relatively soft internal teeth 21, it is possible to reduce damage to the bearing 42, for example, even if the foreign matter X1 gets into the bearing 42. As a result, for example, the amount of hard foreign matter X1 that is generated that would cause significant damage to the bearing 42 is reduced. In particular, when the difference in surface hardness between the internal teeth 21 and the external teeth 31 is a relatively large value, such as HV50 or more, the above effect is remarkable.

[0092] Furthermore, by using spheroidal graphite cast iron as the material for the internal teeth 21, it is possible to expect an effect of suppressing seizure on the tooth surfaces of the internal teeth 21 and the external teeth 31 during initial wear of the internal teeth 21. This provides a lubricating effect at the meshing points between the internal teeth 21 and the external teeth 31, and can improve the power transmission efficiency of the strain wave gear device 1.

[0093] It is not essential that the surface hardness of the internal teeth 21 and the external teeth 31 be specified in terms of Vickers hardness (HV), and the surface hardness of the internal teeth 21 and the external teeth 31 may be specified in terms of other hardnesses, such as Rockwell hardness (HRC), Brinell hardness (HB) or Shore hardness (Hs).

[0094] (4.2) Tooth line modification Next, the tooth trace modification of the internal teeth 21 and the external teeth 31 in this embodiment will be described.

[0095] 5A, 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).

[0096] 5A, the external teeth 31 have tooth bottoms 312 and tooth tips 313. Since the external teeth 31 are provided on the outer peripheral surface of (the body part 321 of) the flexible external gear 3, the tooth bottoms 312 of the external teeth 31 correspond to the outer peripheral surface of (the body part 321 of) the flexible external gear 3, and the tooth tips 313 protrude outward from the outer peripheral surface of (the body part 321 of) the flexible external gear 3.

[0097] 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 D2 (see FIG. 5B ) come into contact with each other, and power is transmitted between the rigid internal gear 2 and the flexible external gear 3.

[0098] 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.

[0099] 5A, 5B, and 6, the internal teeth 21 of the rigid internal gear 2 have tooth trace modification portions 210. That is, 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 embodiment, the tooth trace modification portions 210 are provided at both ends of the internal teeth 21 in the tooth trace direction D1.

[0100] In this embodiment, the external teeth 31 of the flexible external gear 3 also have tooth lead modification portions 310. In other words, in the wave gearing 1, tooth lead modification is performed not only on the internal teeth 21 but also on the external teeth 31. The tooth lead modification portions 210 of the external teeth are provided on at least one end in the tooth lead direction D1. In other words, the external teeth 31 have tooth lead modification portions 310 on at least one end in the tooth lead direction D1 of the external teeth 31. In this embodiment, the tooth lead modification portions 310 are provided on both ends of the external teeth 31 in the tooth lead direction D1.

[0101] As described above, in the wave gearing 1 according to this embodiment, 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 X1 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.

[0102] Here, the tooth trace modification portion 210 is provided at least on the internal teeth 21. By providing the tooth trace modification portion 210 on the rigid internal gear 2 (internal teeth 21), tooth trace modification is unnecessary or the amount of modification can be reduced for the flexible external gear 3 (external teeth 31). This makes it easier to prevent a decrease in strength of the flexible external gear 3 due to tooth trace modification on the flexible external gear 3, which has flexibility. That is, as described above, the flexible external gear 3 is formed from a relatively thin elastic metal body (metal plate), and its relatively small (thin) thickness gives it flexibility. Therefore, if excessive tooth trace modification is performed on the external teeth 31 of the flexible external gear 3, the already thin flexible external gear 3 becomes even thinner, which may lead to a decrease in strength of the flexible external gear 3. In particular, if excessive tooth trace modification is performed on the tooth roots 312 of the external teeth 31, it becomes difficult to ensure the thickness necessary to maintain the strength of the body portion 321. In contrast, in this embodiment, by providing a tooth trace modification portion 210 on the internal tooth 21, the amount of modification for the tooth trace modification of the flexible external gear 3 can be reduced, and as a result, it becomes easier to maintain the strength of the flexible external gear 3.

[0103] Furthermore, in this embodiment, tooth lead modification portions 210, 310 are provided not only on the internal teeth 21 but also on the external teeth 31, i.e., on both the internal teeth 21 and the external teeth 31. Therefore, excessive tooth lead modification is not necessary for the internal teeth 21, and desired performance can be achieved with an appropriate amount of tooth lead modification. In this disclosure, when distinguishing between the tooth lead modification portion 210 of the internal teeth 21 and the tooth lead modification portion 310 of the external teeth 31, the tooth lead modification portion 210 of the internal teeth 21 is also referred to as the "first modification portion 210," and the tooth lead modification portion 310 of the external teeth 31 is also referred to as the "second modification portion 310." That is, in this embodiment, the internal teeth 21 have the first modification portion 210 as the tooth lead modification portion 210. The external teeth 31 have the second modification portion 310, which is a tooth lead modification portion 310 separate from the first modification portion 210.

[0104] When tooth lead modification is performed on both the internal tooth 21 and the external tooth 31, the sum of the modification amount Q1 of the internal tooth 21 and the modification amount Q2 of the external tooth 31 can be considered as the modification amount of the tooth lead modification for the internal tooth 21 and the external tooth 31, as shown in Figure 6. Therefore, if the modification amounts of the tooth lead modification for the internal tooth 21 and the external tooth 31 are the same, the modification amount Q1 of the internal tooth 21 can be reduced by the modification amount Q2 of the external tooth 31 compared to when tooth lead modification is performed on only the internal tooth 21. In Figure 6, the normal tooth lead shape is shown by an imaginary line (two-dot chain line), and the maximum amount of deviation from the normal tooth lead shape due to tooth lead modification is shown as modification amounts Q1 and Q2. In other words, the modification amount Q1 of the internal tooth 21 is the amount of deviation (in the tooth height direction) from the center of the tooth tip 213 in the tooth lead direction D1, as shown in Figure 6. Similarly, the modification amount Q2 of the external tooth 31 is the amount of displacement (in the tooth height direction) from the center in the tooth trace direction D1 of the tooth tip 313. While Fig. 6 illustrates the modification amounts Q1 and Q2 of the tooth tips 213 and 313, the same applies to the modification amounts of not only the tooth tips 213 and 313 but also the tooth bottoms 212 and 312 or one end face in the tooth thickness direction D2.

[0105] As described above, typical processes for tooth trace modification include crowning and relieving. In this embodiment, the tooth trace modification portion (first modification portion) 210 of the internal tooth 21 is formed by crowning. That is, the first modification portion 210 is formed by processing the internal tooth 21 to be rounded toward the center in the tooth trace direction D1 so that the center in the tooth trace direction D1 is convex. Similarly, the tooth trace modification portion (second modification portion) 310 of the external tooth 31 is also formed by crowning. That is, the second modification portion 310 is formed by processing the external tooth 31 to be rounded toward the center in the tooth trace direction D1 so that the center in the tooth trace direction D1 is convex. Thus, in this embodiment, the first modification portion 210 and the second modification portion 310 include the same type of modification. That is, the first modification portion 210 and the second modification portion 310 are both tooth trace modification of the same type (here, crowning).

[0106] Furthermore, the tooth trace modification portion (first modification portion) 210 of the internal tooth 21 includes an inclined surface inclined with respect to the tooth trace direction D1 on at least one of the bottom 212, the tip 213, and one end face in the tooth thickness direction D2 of the internal tooth 21. That is, the tooth trace modification portion 210 is formed by applying a tooth trace modification process (here, crowning) to at least one of the bottom 212, the tip 213, and one end face in the tooth thickness direction D2 of the internal tooth 21. In the case of tooth trace modification of the bottom 212, an inclined surface inclined with respect to the tooth trace direction D1 is formed on the bottom 212 so that the bottom 212 becomes lower as it approaches both ends in the tooth trace direction D1. In the case of tooth trace modification of the tooth tip 213, an inclined surface inclined with respect to the tooth trace direction D1 is formed on the tip 213 so that the tooth tip 213 becomes lower as it approaches both ends in the tooth trace direction D1. In the case of tooth lead modification on one end face in the tooth thickness direction D2, an inclined surface inclined with respect to the tooth lead direction D1 is formed on one end face in the tooth thickness direction D2 so that the tooth thickness becomes smaller toward both ends in the tooth lead direction D1. In this embodiment, as shown in Figures 5A and 5B, tooth lead modification is performed on the bottom 212, the tip 213, and all of the end faces in the tooth thickness direction D2 of the internal tooth 21.

[0107] In particular, by including an inclined surface at least on the tooth bottom 212 of the tooth lead modification portion 210, it is easy to avoid interference between the tooth tip 313 of the external tooth 31 and the tooth bottom 212 of the internal tooth 21. In other words, when tooth lead modification is performed on the tooth bottom 212 of the internal tooth 21, a gap for "escape" of the tooth tip 313 of the external tooth 31 can be secured, and excessive stress concentration due to interference between the tooth tip 313 of the external tooth 31 and the tooth bottom 212 of the internal tooth 21 is less likely to occur.

[0108] Similarly, for the external tooth 31, the tooth lead modification portion (second modification portion) 310 includes an inclined surface inclined with respect to the tooth lead direction D1 on at least one of the tooth bottom 312, tooth tip 313, and one end face in the tooth thickness direction D2 of the external tooth 31. In other words, the tooth lead modification portion 310 is formed by applying tooth lead modification processing (here, crowning) to at least one of the tooth bottom 312, tooth tip 313, and one end face in the tooth thickness direction D2 of the external tooth 31. In this embodiment, as shown in Figures 5A and 5B, tooth lead modification is applied to all of the tooth bottom 312, tooth tip 313, and both end faces in the tooth thickness direction D2 of the external tooth 31.

[0109] As shown in FIG. 5B , due to the tooth trace modification applied to both end faces in the tooth thickness direction D2, the tooth thickness of each of the internal teeth 21 and the external teeth 31 is greatest at the center in the tooth trace direction D1 and gradually decreases toward both ends in the tooth trace direction D1. Therefore, at the meshing position between the internal teeth 21 and the external teeth 31, the gap between the internal teeth 21 and the external teeth 31 is smallest in the center in the tooth trace direction D1 where no tooth trace modification (here, crowning) has been applied. The portions of the internal teeth 21 and the external teeth 31 in the tooth trace direction D1 where no tooth trace modification has been applied, i.e., the portions where the normal tooth trace shape remains, are also referred to as "unmodified portions." Therefore, basically, at the meshing position between the internal teeth 21 and the external teeth 31, the internal teeth 21 and the external teeth 31 first come into contact at the "unmodified portions" located in the center in the tooth trace direction D1.

[0110] 7A to 7C, the gap G1 between the internal teeth 21 and the external teeth 31 is smallest in FIG. 7A, which is a cross section of the center in the tooth trace direction D1. In other words, the gap G1 between the internal teeth 21 and the external teeth 31 increases in the order of FIG. 7B and FIG. 7C toward one end of the tooth trace direction D1 (the output side of the rotation axis Ax1). In this way, tooth trace modification causes the tooth flank to gradually shift in the negative direction as it moves away from the center in the tooth trace direction D1, and therefore the gap G1 between the internal teeth 21 and the external teeth 31 increases.

[0111] In this embodiment, such an unmodified portion (the center in the tooth trace direction D1) is arranged in a position in the tooth trace direction D1 that overlaps with the rolling elements 423 of the bearing 42. Strictly speaking, the unmodified portion (the center in the tooth trace direction D1) is located on a line (a virtual line) that is perpendicular to the rotation axis Ax1 and passes through the center of the rolling elements 423. As a result, stress transmitted from the multiple rolling elements 423 to the flexible external gear 3 via the outer ring 421 of the bearing 42 acts mainly on the unmodified portion, making it easier for the internal teeth 21 and the external teeth 31 to come into contact initially at the unmodified portion.

[0112] In this embodiment, there is a difference in the modification amounts Q1, Q2 between the first modification portion 210 of the internal teeth 21 and the second modification portion 310 of the external teeth 31. The modification amount Q2 of the second modification portion 310 is smaller than the modification amount Q1 of the first modification portion 210 (Q1 > Q2). The flexible external gear 3 has an elastic deformation (flexion) function in addition to its power transmission function, and since stress caused by flexion is inherent, the external teeth 31 of the flexible external gear 3 are required to be resistant to bending stress. Furthermore, when tooth trace modification is applied to the external teeth 31, the roots of the external teeth 31 basically become thinner, reducing the resistance to bending stress and the durability of the flexible external gear 3. On the other hand, since the rigid internal gear 2 does not need to bend elastically, the internal teeth 21 of the rigid internal gear 2 are not required to be resistant to bending stress. Therefore, even if the tooth lead modification is performed on the internal teeth 21 and the root of the internal teeth 21 becomes thin, this has almost no effect on the durability of the rigid internal gear 2. Therefore, by making the modification amount Q2 of the external teeth 31 smaller than the modification amount Q1 of the internal teeth 21, it is possible to prevent a decrease in the durability of the strain wave gear device 1 while ensuring a sufficient modification amount for the tooth lead modification of the internal teeth 21 and external teeth 31.

[0113] Furthermore, the tooth trace modifiers 210 are provided at both ends of the internal teeth 21 in the tooth trace direction D1. In other words, the tooth trace modifiers 210 are provided at both ends of the internal teeth 21 on the input side and the output side of the rotation axis Ax1. That is, the tooth trace modifiers 210 are provided at least at the end of the internal teeth 21 on the opening surface 35 side in the tooth trace direction D1. Here, 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 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, a tapered surface 302 (see FIG. 8A ) inclined with respect to the rotation axis Ax1 is formed on the inner circumferential surface 301 of the body portion 321 of the flexible external gear 3. Furthermore, by providing the tooth trace modification portion 210 on the opening surface 35 side in the tooth trace direction D1, it becomes possible to modify the tooth trace of the internal tooth 21 so as to allow (avoid) the inclined external tooth 31 by such a tapered surface 302. Therefore, even at the end portion on the opening surface 35 side in the tooth trace direction D1 where stress concentration due to deformation of the external tooth 31 is particularly likely to occur, the tooth trace modification portion 210 can make it difficult for stress concentration to occur.

[0114] The tooth trace modification portion (first modification portion) 210 of the internal teeth 21 is formed, for example, using a skiving cutter. That is, the tooth trace modification portion 210 can be formed on the internal teeth 21 formed on the inner peripheral surface of the rigid internal gear 2 by tooth trace modification using a skiving cutter. The skiving cutter has multiple pinion gear-shaped cutting blades that form a gear portion (internal teeth 21) on the workpiece (rigid internal gear 2). The skiving cutter is driven to rotate about a cutter axis that is offset from the workpiece axis, and cuts the workpiece by moving relatively along the tooth trace direction D1 while rotating synchronously with the workpiece. As a result, a gear portion (internal teeth 21) with tooth trace modification is formed on the workpiece (rigid internal gear 2).

[0115] Furthermore, in this embodiment, the internal teeth 21 and the external teeth 31 are subjected to not only the tooth trace modification described above but also tooth profile modification as shown in FIGS. 7A to 7C . The amount of tooth profile modification is determined to satisfy the following condition when the flexible external gear 3, undergoing elastic deformation, is positioned inside the rigid internal gear 2 and power is not being transmitted. Specifically, the condition is that no gap occurs near the pitch point at the meshing position of the internal teeth 21 and the external teeth 31, and a gap of, for example, about 0.1 module or more occurs between the tip 313 of the external tooth 31 and the bottom 212 of the internal tooth 21. To satisfy this condition, the internal teeth 21 and the external teeth 31 are modified to have a rounded shape toward the center in the tooth height direction so that the center is convex in the tooth height direction. This makes it less likely for bottom contact to occur even if the internal teeth 21 of the rigid internal gear 2 wear.

[0116] (4.3) Face width Next, the tooth widths (dimensions in the tooth trace direction D1) of the internal teeth 21 and external teeth 31 in this embodiment will be described.

[0117] 5A, in this embodiment, the external teeth 31 of the flexible external gear 3 protrude in at least one direction in the tooth trace direction D1 relative to the internal teeth 21 of the rigid internal gear 2. That is, as described above, 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 at the same position in the direction of the rotation axis Ax1. 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 tooth trace direction D1, the internal teeth 21 are contained within the range of the tooth trace of the external teeth 31, and the external teeth 31 protrude in at least one direction in the tooth trace direction D1 relative to the internal teeth 21.

[0118] In particular, in this embodiment, as shown in FIG. 5A, the external teeth 31 protrude relative to the internal teeth 21 on both sides of the tooth trace direction D1 (the input side and the output side of the rotation axis Ax1). Toward one side of the tooth trace direction D1 (the input side of the rotation axis Ax1), the external teeth 31 protrude by a protrusion amount L1 from the edge of the internal teeth 21. Toward the other side of the tooth trace direction D1 (the output side of the rotation axis Ax1), the external teeth 31 protrude by a protrusion amount L2 from the edge of the internal teeth 21. In this embodiment, as an example, the protrusion amounts L1 and L2 of the external teeth 31 from the internal teeth 21 are substantially the same on both sides of the tooth trace direction D1.

[0119] Here, the protrusion amounts L1 and L2 are expressed by comparing a portion of the internal tooth 21 excluding the chamfered portion 211 with a portion of the external tooth 31 excluding the chamfered portion 311. In other words, on one side of the tooth trace direction D1 (the input side of the rotation axis Ax1), the distance from the start point of the chamfered portion 211 of the internal tooth 21 to the start point of the chamfered portion 311 of the external tooth 31 is the protrusion amount L1. Similarly, on the other side of the tooth trace direction D1 (the output side of the rotation axis Ax1), the distance from the start point of the chamfered portion 211 of the internal tooth 21 to the start point of the chamfered portion 311 of the external tooth 31 is the protrusion amount L2.

[0120] As explained in the section "(4.1) Surface Hardness," the surface hardness of the internal teeth 21 is lower than that of the external teeth 31. In this embodiment, the external teeth 31, which have a relatively high surface hardness, protrude from the internal teeth 21 in at least one direction in the tooth trace direction D1. This means that steps due to wear are unlikely to occur on the tooth surfaces of the internal teeth 21 in at least one direction in the tooth trace direction D1. In other words, the internal teeth 21, which have a relatively low surface hardness, wear uniformly due to contact with the external teeth 31 in at least one direction in the tooth trace direction D1, making it difficult for localized depressions (steps) to occur on the tooth surfaces of the internal teeth 21. Therefore, even if the tooth contact position shifts in the tooth trace direction D1 due to some kind of accident, it is easy to prevent abnormalities in the strain wave gear device 1 caused by excessive loads being applied to the meshing areas between the internal teeth 21 and the external teeth 31. This makes it difficult for foreign matter X1 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 strain wave gear device 1 that is less susceptible to reduced reliability.

[0121] Furthermore, the external teeth 31 protrude in both directions in the tooth trace direction D1 relative to the internal teeth 21. That is, the external teeth 31 protrude at least toward the opening surface 35 in the tooth trace direction D1 relative to the internal teeth 21. Here, 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 is more deformed than the end on the bottom 322 side, and becomes more elliptical. 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, a tapered surface 302 (see FIG. 8A ) inclined with respect to the rotation axis Ax1 is generated on the inner circumferential surface 301 of the body portion 321 of the flexible external gear 3. Furthermore, because the external teeth 31 protrude from the internal teeth 21 on the opening surface 35 side in the tooth trace direction D1, it is possible to prevent contact between the internal teeth 21 and the corners of the inclined tips of the external teeth 31 due to the tapered surfaces 302. Therefore, even at the end on the opening surface 35 side in the tooth trace direction D1 where stress concentration due to deformation of the external teeth 31 is particularly likely to occur, localized depressions (steps) are unlikely to occur on the tooth surfaces of the internal teeth 21.

[0122] (4.4) Tapered surface Next, the tapered surface 302 formed on the inner peripheral surface 301 of the flexible external gear 3, which corresponds to the back side of the external teeth 31, will be described.

[0123] As described above, 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 is deformed more greatly than the end on the bottom portion 322 side, and assumes a shape closer to an ellipse. Therefore, 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 302 that is inclined with respect to the rotation axis Ax1, as shown in Figures 8A and 8B.

[0124] The tapered surface 302 is inclined by an inclination angle θ1 with respect to the rotation axis Ax1. Due to the formation of such a tapered surface 302, the gap between the inner peripheral surface 301 (tapered surface 302) and an outer peripheral surface 424 (see FIG. 8B ) of the outer ring 421 of the bearing 42 of the wave generator 4 fitted inside the body portion 321 gradually increases toward the opening surface 35. In short, the inner peripheral surface 301 of the flexible external gear 3 has, at a location facing the outer peripheral surface 424 of (the outer ring 421 of) the wave generator 4, a tapered surface 302 that increases the gap with the outer peripheral surface 424 of the wave generator 4 in one direction along the rotation axis Ax1 (toward the opening surface 35).

[0125] Here, the inclination angle θ1 of the tapered surface 302 with respect to the rotation axis Ax1 is 5 degrees or less. Therefore, the gap that occurs between the tapered surface 302 and the outer peripheral surface 424 of the wave generator 4 is a very small gap. In this embodiment, the very small gap that occurs between the tapered surface 302 and the outer peripheral surface 424 of the wave generator 4 is used to hold the lubricant Lb1. Specifically, the very small gap between the tapered surface 302 and the outer peripheral surface 424 of the wave generator 4 can hold the lubricant Lb1 in a liquid or gel state.

[0126] That is, in the wave gear device 1 according to this embodiment, 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, etc. As an example, the lubricant Lb1 is a liquid lubricant (oil). When the wave gear device 1 is in use, the lubricant Lb1 also enters between the outer ring 421 (outer peripheral surface 424) of the bearing 42 and the tapered surface 302 of the flexible external gear 3, as shown in FIG. 8B. As a result, the lubricant Lb1 seals the gap between the outer peripheral surface 424 and the tapered surface 302.

[0127] Here, with respect to the bearing 42 of the wave generator 4, the space on the input side (right side in FIG. 8A ) of the rotating shaft Ax1 and the space on the output side (left side in FIG. 8A ) of the rotating shaft Ax1 can be connected through the gap between the outer circumferential surface 424 and the tapered surface 302. In this way, the gap forming a bottleneck connecting the outside (input side of the rotating shaft Ax1) and inside (output side of the rotating shaft Ax1) of the wave generator 4 is filled with the lubricant Lb1. Therefore, the space on the input side of the rotating shaft Ax1 and the space on the output side of the rotating shaft Ax1 are shielded by the lubricant Lb1. Therefore, as shown in FIG. 8B , the lubricant Lb1 prevents foreign matter X1 from entering the inside of the wave generator 4 from one side (input side) of the rotating shaft Ax1.

[0128] That is, in this embodiment, the lubricant Lb1 is held in the gap between the tapered surface 302 and the outer peripheral surface 424 of the wave generator 4. More specifically, as shown in FIG. 8B , the lubricant Lb1 is held in the minute gap between the tapered surface 302 and the outer peripheral surface 424 of the wave generator 4 by capillary action. Therefore, the gap between the tapered surface 302 and the outer peripheral surface 424 of the wave generator 4 is maintained in a state where it is filled with the lubricant Lb1. The magnitude of the holding force due to capillary action also varies depending on the "wettability" between the tapered surface 302 and the outer peripheral surface 424 and the lubricant Lb1. Therefore, it is preferable that at least the tapered surface 302 and the outer peripheral surface 424 do not have oil repellency.

[0129] The inclination angle θ1 of the tapered surface 302 with respect to the rotation axis Ax1 is not limited to 5 degrees or less, and may be, for example, 10 degrees or less, 15 degrees or less, or 20 degrees or less. Furthermore, holding the lubricant Lb1 in the gap between the tapered surface 302 and the outer peripheral surface 424 of the wave generator 4 is not an essential configuration for the wave gear device 1, and the lubricant Lb1 does not have to be held in that gap.

[0130] (5) Effect Next, the operation of the strain wave gear device 1 according to this embodiment will be described in more detail.

[0131] In the strain wave gearing 1, the internal teeth 21 and the external teeth 31 are partially meshed with each other while the flexible external gear 3 is elastically deformed. Therefore, the meshing between the internal teeth 21 and the external teeth 31 involves "slip" in both the tooth profile direction (the direction perpendicular to the tooth trace direction D1) and the tooth trace direction D1. In the range of rotational speeds of the relative rotation of the two gears (the rigid internal gear 2 and the flexible external gear 3) during normal use of the strain wave gearing 1, the flow rate of the lubricant Lb1 is relatively low. Therefore, in the meshing region between the internal teeth 21 and the external teeth 31, the lubricant Lb1 flows at a relatively low rate in both the tooth profile direction and the tooth trace direction D1, making it difficult for the lubricant Lb1 to flush foreign matter X1 generated between the internal teeth 21 and the external teeth 31 out of the strain wave gearing 1. Therefore, once foreign matter X1 is generated, it tends to remain inside the strain wave gear device 1, and if such foreign matter X1 gets into the bearing 42, etc., it can cause surface-originating flaking, which leads to a decrease in the reliability of the strain wave gear device 1, as described above.

[0132] One possible solution to this decline in reliability of the strain wave gear device 1 is to block (seal) the side surface of the bearing 42 with a sealing member to prevent foreign matter X1 from entering the bearing 42. However, a sealing member used in a bearing 42 that has a relatively high reduction ratio and is elastically deformable will have a large friction loss, making it difficult to extend its lifespan, and will also pose a problem of reduced power transmission efficiency. Another possible solution is to increase the surface hardness of the outer ring 421 and the inner ring 422 of the bearing 42 by subjecting them to a heat treatment such as carbonitriding, which is resistant to micropitting damage. However, there is a problem in that the surface hardness of the outer ring 421 and the inner ring 422 cannot be increased significantly so as not to inhibit the elastic deformation of the bearing 42.

[0133] In contrast, the wave gear device 1 according to this embodiment makes it difficult for the foreign matter X1 to be generated in the first place, thereby eliminating the problems that can arise from measures such as those described above for the bearing 42. In other words, suppressing the generation of the foreign matter X1 itself, as in this embodiment, is particularly useful for the wave gear device 1, which not only makes it less likely that the reliability of the wave gear device 1 will decrease, but also has the advantage of making it easier to extend the lifespan and improve power transmission efficiency.

[0134] As an example, if flaking occurs on the inner peripheral surface (rolling surface) of the outer ring 421 due to the ingress of foreign matter X1, it could impair the function of the bearing 42 and interfere with the operation of the strain wave gear device 1. In the strain wave gear device 1 according to this embodiment, by making it difficult for foreign matter X1 to form in the first place, it is possible to dramatically reduce the likelihood of foreign matter X1 becoming caught in the bearing 42, thereby improving the reliability of the strain wave gear device 1. In particular, since reliability is less likely to decrease even during long-term use, this also leads to a longer life and higher performance of the strain wave gear device 1.

[0135] Furthermore, in the strain wave gearing 1, the surface hardness of the internal teeth 21 is lower than that of the external teeth 31. Therefore, when the face width of the internal teeth 21 is greater than that of the external teeth 31 and the external teeth 31 fit within the tooth trace of the internal teeth 21, a localized depression (step) may occur in part of the tooth flank of the internal teeth 21 in the tooth trace direction D1 due to wear caused by contact with the external teeth 31. If such a depression occurs and the tooth contact position shifts in the tooth trace direction (a direction parallel to the rotation axis Ax1) for some reason, excessive load is applied to the meshing area between the internal teeth 21 and the external teeth 31, which may lead to an abnormality in the strain wave gearing 1. In other words, even if the external teeth 31 have a relatively high surface hardness, if a corner such as one end in the tooth trace direction D1 comes into contact with the step of the internal teeth 21, that corner may chip off, resulting in a hard (relatively hard) foreign object X1.

[0136] In contrast, in the wave gearing 1 according to this embodiment, the external teeth 31 protrude relative to the internal teeth 21 in at least one direction in the tooth trace direction D1. As a result, on at least one side in the tooth trace direction D1, the internal teeth 21, which have a relatively low surface hardness, wear uniformly due to tooth contact with the external teeth 31, making it difficult for localized depressions (steps) to form on the tooth surfaces of the internal teeth 21. Therefore, even if the tooth contact position shifts in the tooth trace direction D1 due to some kind of accident, it is easy to prevent abnormalities in the wave gearing 1 caused by excessive load being applied to the meshing area between the internal teeth 21 and the external teeth 31. In other words, chipping is unlikely to occur in corners such as one end of the external teeth 31 in the tooth trace direction D1, and as a result, hard (relatively hard) foreign matter X1 is unlikely to form.

[0137] Furthermore, the basic structure of the wave gearing 1 has a relatively large number of simultaneously meshing teeth between the internal teeth 21 and the external teeth 31. While this has the advantage of distributing the meshing load, it also has the advantage of relatively large slippage associated with meshing, which can lead to significant meshing loss. Such meshing loss can be a factor in deteriorating the startability of the wave gearing 1, particularly in low-temperature environments where the lubricant Lb1 is likely to harden. In contrast, the wave gearing 1 of this embodiment has a tooth trace modification portion 210 at least at the end of the internal teeth 21 on the opening surface 35 side in the tooth trace direction D1. This reduces meshing between the internal teeth 21 and the external teeth 31 at the end on the opening surface 35 side, where the amount of slippage in the tooth trace direction D1 is particularly large. This reduces meshing loss and improves power transmission efficiency. In this way, the wave gearing 1 of this embodiment not only has a longer life, but also improves power transmission efficiency, thereby improving the startability of the wave gearing 1, for example, in low-temperature environments where the lubricant Lb1 is likely to harden.

[0138] (6) Application Examples Next, an application example of the strain wave gear device 1 and actuator 100 according to this embodiment will be described with reference to FIG.

[0139] 9 is a cross-sectional view showing an example of a robot 9 using the strain wave gear device 1 according to this embodiment. This robot 9 is a horizontally articulated robot, a so-called SCARA (Selective Compliance Assembly Robot Arm) type robot.

[0140] As shown in FIG. 9, the robot 9 is equipped with two strain wave gearings 1 and a link 91. The two strain wave gearings 1 are provided at two joints on the robot 9, respectively. The link 91 connects the two joints. In the example of FIG. 9, the strain wave gearing 1 is a top hat type strain wave gearing rather than a cup type strain wave gearing. In other words, the strain wave gearing 1 illustrated in FIG. 9 uses a flexible external gear 3 formed in a top hat shape.

[0141] (7) Variations 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.

[0142] 10A to 10D show a modified example of embodiment 1, and are drawings showing the relationship between the internal teeth 21 and the external teeth 31, corresponding to the cross-sectional view taken along line A1-A1 in Fig. 5A. Hatching (diagonal lines) of the cross section is omitted in Figs. 10A to 10D.

[0143] 10A, the tooth trace modification portion (first modification portion) 210 of the internal tooth 21 is formed only on one end face of both end faces of the internal tooth 21 in the tooth thickness direction D2 that is on the rotational direction R1 side of the flexible external gear 3. Furthermore, the tooth trace modification portion (second modification portion) 310 of the external tooth 31 is formed only on one end face of both end faces of the external tooth 31 in the tooth thickness direction D2 that is on the opposite side to the rotational direction R1 of the flexible external gear 3. As a result, during power transmission, the tooth surfaces of the internal tooth 21 and the external tooth 31 on which the tooth trace modification portions 210, 310 are formed come into contact with each other, and therefore the same effect as in the first embodiment can be expected.

[0144] In a second modified example shown in Fig. 10B, the tooth trace modifying portion (first modifying portion) 210 of the internal tooth 21 is formed only on one end face of the internal tooth 21 in the tooth thickness direction D2, which is on the rotational direction R1 side of the flexible external gear 3. Furthermore, the tooth trace modifying portion (second modifying portion) 310 of the external tooth 31 is formed only on one end face of the external tooth 31 in the tooth thickness direction D2, which is on the rotational direction R1 side of the flexible external gear 3. Even with this configuration, the tooth trace modifying portions 210, 310 can be expected to provide the same effects as in embodiment 1.

[0145] In a third modified example shown in Fig. 10C, of ​​the internal teeth 21 and the external teeth 31, a tooth lead modification portion (first modification portion) 210 is provided only on the internal teeth 21, and no tooth lead modification portion is provided on the external teeth 31. Even with this configuration, the tooth lead modification portion 210 can be expected to provide the same effect as in embodiment 1. As yet another example, of the internal teeth 21 and the external teeth 31, a tooth lead modification portion (second modification portion) 310 may be provided only on the external teeth 31, and no tooth lead modification portion may be provided on the internal teeth 21.

[0146] In a fourth modified example shown in Fig. 10D, a tooth lead modification portion (first modification portion) 210 is provided only at one end of the internal tooth 21 in the tooth lead direction D1, and a tooth lead modification portion (second modification portion) 310 is provided only at one end of the external tooth 31 in the tooth lead direction D1. In the example of Fig. 10D, both of the tooth lead modification portions 210, 310 are provided at the end on the opening surface 35 side in the tooth lead direction D1. As yet another example, at least one of the tooth lead modification portions 210, 310 may be provided at the end on the opposite side from the opening surface 35 in the tooth lead direction D1.

[0147] 10A to 10D can be combined as appropriate. For example, by combining the third and fourth modifications, the tooth trace modification portion 210 may be provided only on the internal tooth 21 of the internal tooth 21 and the external tooth 31, and the tooth trace modification portion 210 may be provided only on one end of the internal tooth 21 in the tooth trace direction D1.

[0148] Furthermore, it is not essential for the wave gear device 1 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.

[0149] Furthermore, the configuration in which the internal teeth 21 have the tooth trace modification portions 210 and the configuration in which the surface hardness of the internal teeth 21 is lower than that of the external teeth 31 and the external teeth 31 protrude relative to the internal teeth 21 in at least one direction in the tooth trace direction D1 can be independently adopted. In other words, even with the configuration in which the surface hardness of the internal teeth 21 is lower than that of the external teeth 31 and the external teeth 31 protrude relative to the internal teeth 21 in at least one direction in the tooth trace direction D1 alone, foreign matter X1 is less likely to be generated due to chipping, wear, or the like caused by contact between the internal teeth 21 and the external teeth 31. Therefore, it is possible to realize a strain wave gear device 1 in which reliability is less likely to decrease even if the internal teeth 21 do not have the tooth trace modification portions 210. On the other hand, even with the configuration in which the internal teeth 21 have the tooth trace modification portions 210 alone, foreign matter X1 is less likely to be generated due to chipping, wear, or the like caused by contact between the internal teeth 21 and the external teeth 31. Therefore, even if the external teeth 31 do not protrude relative to the internal teeth 21 in at least one direction in the tooth trace direction D1, it is possible to realize a strain wave gear device 1 that is less likely to experience a decrease in reliability.

[0150] Furthermore, the configuration for holding the lubricant Lb1 in the gap between the tapered surface 302 and the outer peripheral surface 424 of the wave generator 4 can also be adopted alone. In other words, even if the internal teeth 21 do not have the tooth trace modification portions 210 and the external teeth 31 do not protrude in at least one direction in the tooth trace direction D1 relative to the internal teeth 21, the lubricant Lb1 can be held in the gap between the tapered surface 302 and the outer peripheral surface 424 of the wave generator 4.

[0151] Furthermore, the strain wave gearing 1 is not limited to the cup type described in the first embodiment, and may be, for example, a top hat type, a ring type, a differential type, a flat type (pancake type), or a shield type. For example, even a top hat type strain wave gearing 1 as illustrated in FIG. 9 has a cylindrical flexible external gear 3 that has an opening surface 35 on one side in the tooth trace direction D1, just like a cup type. In other words, the top hat type flexible external gear 3 has a flange portion on one end on the rotation axis Ax1 side and an opening surface 35 on the end opposite the flange portion. Even the top hat type flexible external gear 3 has external teeth 31 on the end on the opening surface 35 side, and a wave generator 4 is fitted into it.

[0152] 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.

[0153] Furthermore, application examples of the strain wave gear device 1 and actuator 100 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.

[0154] Furthermore, bearing 42 is not limited to a deep groove ball bearing, but may be, for example, an angular contact ball bearing, etc. Furthermore, bearing 42 is not limited to a ball bearing, but may be, for example, a roller bearing in which rolling elements 423 are formed of "rollers" that are not ball-shaped, such as a cylindrical roller bearing, a needle roller bearing, or a tapered roller bearing.

[0155] Furthermore, the material of each component of the strain wave gear device 1 or the actuator 100 is not limited to metal, but may be, for example, a resin such as engineering plastic.

[0156] 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.

[0157] Furthermore, the protrusion amounts L1, L2 of the external teeth 31 from the internal teeth 21 do not necessarily have to be substantially the same on both sides of the tooth trace direction D1. For example, the protrusion amount L1 on one side of the tooth trace direction D1 (the input side of the rotation axis Ax1) may be greater than the protrusion amount L2 on the other side of the tooth trace direction D1 (the output side of the rotation axis Ax1). Conversely, the protrusion amount L1 on one side of the tooth trace direction D1 (the input side of the rotation axis Ax1) may be smaller than the protrusion amount L2 on the other side of the tooth trace direction D1 (the output side of the rotation axis Ax1).

[0158] Furthermore, it is not an essential configuration of the wave gear device 1 that the modification amount Q2 of the second modifying portion 310 is smaller than the modification amount Q1 of the first modifying portion 210. For example, the modification amount Q2 of the second modifying portion 310 may be equal to the modification amount Q1 of the first modifying portion 210 (Q1=Q2), or may be larger than the modification amount Q1 of the first modifying portion 210 (Q1=Q2). <Q2)。

[0159] (Embodiment 2) 11A to 12C, the wave gear device 1A according to this embodiment differs from the wave gear device 1 according to embodiment 1 in that the tooth trace modification portions (first modification portions) 210 of the internal teeth 21 are formed by relieving. Hereinafter, common reference numerals will be used to designate components similar to those in embodiment 1, and explanations will be omitted where appropriate.

[0160] Fig. 11A is a cross-sectional view focusing on the internal teeth 21 and the external teeth 31, Fig. 11B is a cross-sectional view taken along line A1-A1 in Fig. 11A, Fig. 12A is a cross-sectional view taken along line B1-B1 in Fig. 11A, Fig. 12B is a cross-sectional view taken along line B2-B2 in Fig. 11A, and Fig. 12C is a cross-sectional view taken along line B3-B3 in Fig. 11A.

[0161] The tooth trace modification portion (first modification portion) 210 of the internal tooth 21 is formed by crowning in the first embodiment, whereas in this embodiment it is formed by relieving. That is, the first modification portion 210 is formed by tapering only both end portions in the tooth trace direction D1 so that the central portion in the tooth trace direction D1 is convex with respect to the internal tooth 21, while the central portion in the tooth trace direction D1 remains in the normal tooth trace shape. In this embodiment, the tooth trace modification portion (second modification portion) 310 of the external tooth 31 is also formed by relieving. In this way, both the first modification portion 210 and the second modification portion 310 are tooth trace modified by the same type (here, relieving).

[0162] 11A and 11B, tooth trace modification consisting of relieving is applied to all of the bottoms 212, tops 213, and both end faces in the tooth thickness direction D2 of the internal teeth 21. Similarly, tooth trace modification consisting of relieving is applied to all of the bottoms 312, tops 313, and both end faces in the tooth thickness direction D2 of the external teeth 31.

[0163] 11B, with the tooth trace modification portions 210, 310 as described above, the tooth thickness of each of the internal teeth 21 and external teeth 31 is greatest at the center in the tooth trace direction D1, and after the start point of relieving, it gradually becomes smaller toward both ends in the tooth trace direction D1. Therefore, at the meshing position of the internal teeth 21 and the external teeth 31, the gap between the internal teeth 21 and the external teeth 31 is smallest in the tooth trace direction D1 at the center (non-modified portion) where no tooth trace modification (relieving here) has been applied.

[0164] 12A to 12C, the gap G1 between the internal teeth 21 and the external teeth 31 is smallest in FIG. 12A, which is a cross section at the start point of relieving in the tooth trace direction D1. In other words, the gap G1 between the internal teeth 21 and the external teeth 31 increases in the order of FIG. 12B and FIG. 12C toward one end of the tooth trace direction D1 (the output side of the rotation axis Ax1). In this way, due to tooth trace modification, the tooth flank gradually shifts in the negative direction as it moves away from the center in the tooth trace direction D1, and therefore the gap G1 between the internal teeth 21 and the external teeth 31 increases.

[0165] As a modification of the second embodiment, for example, the first modification portion 210 and the second modification portion 310 may be different types of tooth trace modification, such as the first modification portion 210 being a relieving portion and the second modification portion 310 being a crowning portion. Conversely, the first modification portion 210 may be a crowning portion and the second modification portion 310 being a relieving portion.

[0166] The configuration of the second embodiment (including modifications) can be applied in appropriate combination with the configuration described in the first embodiment (including modifications).

[0167] (Embodiment 3) As shown in Fig. 13, the wave gear device 1B according to this embodiment differs from the wave gear device 1 according to embodiment 1 in that the external teeth 31 protrude only in one direction in the tooth trace direction D1 relative to the internal teeth 21. Fig. 13 is a cross-sectional view focusing on the internal teeth 21 and external teeth 31, and hatching (diagonal lines) of the cross section has been omitted. Below, common reference numerals are used for configurations that are the same as those in embodiment 1, and explanations will be omitted as appropriate.

[0168] That is, whereas in the first embodiment the external teeth 31 protrude in both directions in the tooth trace direction D1 (on the input side and the output side of the rotation axis Ax1) relative to the internal teeth 21, in this embodiment they protrude in only one direction in the tooth trace direction D1 relative to the internal teeth 21. In particular, in this embodiment, the external teeth 31 protrude toward the opening surface 35 in the tooth trace direction D1, i.e., toward the input side of the rotation axis Ax1, relative to the internal teeth 21. That is, in this embodiment, the external teeth 31 protrude toward the opening surface 35 in the tooth trace direction D1 (the input side of the rotation axis Ax1) relative to the internal teeth 21, and do not protrude toward the opposite side of the opening surface 35 in the tooth trace direction D1 (the output side of the rotation axis Ax1).

[0169] Here, when elastic deformation occurs in the flexible external gear 3, the flexible external gear 3 deforms more greatly at the end on the opening surface 35 side in the direction of the rotation axis Ax1 than at the end on the bottom 322 side, and assumes a shape closer to an ellipse. As in this embodiment, the external teeth 31 protrude from the internal teeth 21 on the opening surface 35 side in the tooth trace direction D1, and this tapered surface 302 makes it possible to avoid contact between the internal teeth 21 and the corners of the inclined tips of the external teeth 31. Therefore, with the configuration of this embodiment, localized depressions (steps) are less likely to occur on the tooth surfaces of the internal teeth 21 at the end on the opening surface 35 side in the tooth trace direction D1, where stress concentration due to deformation of the external teeth 31 is particularly likely to occur.

[0170] As a modification of the third embodiment, the external teeth 31 may protrude only on the side opposite the opening surface 35 in the tooth trace direction D1 relative to the internal teeth 21, i.e., only on the output side of the rotation axis Ax1. In this case, the external teeth 31 do not protrude on the opening surface 35 side (input side of the rotation axis Ax1) relative to the internal teeth 21 in the tooth trace direction D1.

[0171] The configuration of the third embodiment (including modifications) can be applied in appropriate combination with the configurations (including modifications) described in the first or second embodiment.

[0172] (summary) As described above, the wave gearing (1, 1A, 1B) 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) is disposed inside the flexible external gear (3) and generates a deflection in the flexible external gear (3). The strain wave gearing (1, 1A, 1B) deforms the flexible external gear (3) in response to rotation of the wave generator (4) about the rotation axis (Ax1), causing some of the external teeth (31) to mesh with some of the internal teeth (21), causing the flexible external gear (3) to rotate relative to the rigid internal gear (2) in accordance with the difference in the number of teeth between the rigid internal gear (2). The surface hardness of the internal teeth (21) is lower than that of the external teeth (31). The external teeth (31) protrude in at least one tooth trace direction (D1) relative to the internal teeth (21).

[0173] According to this embodiment, steps due to wear are unlikely to occur on the tooth flanks of the internal teeth (21) at least in one direction of the tooth trace (D1). That is, at least in one direction of the tooth trace (D1), the internal teeth (21), which have a relatively low surface hardness, are uniformly worn by contact with the external teeth (31). This makes it difficult for localized depressions (steps) to occur on the tooth flanks of the internal teeth (21). Therefore, even if the tooth contact position shifts in the tooth trace direction (D1) due to some kind of accident, it is easy to prevent abnormalities in the strain wave gearing (1, 1A, 1B) caused by excessive load being applied to the meshing portion between the internal teeth (21) and the external teeth (31). That is, chipping is unlikely to occur in corner portions, such as at one end of the external teeth (31) in the tooth trace direction (D1). As a result, hard (relatively hard) foreign matter (X1) is unlikely to occur. Therefore, foreign matter (X1) is less likely to be generated due to chipping or wear caused by contact between the internal teeth (21) and the external teeth (31), and it is possible to provide a strain wave gear device (1, 1A, 1B) that is less likely to experience a decrease in reliability.

[0174] In the wave gear device (1, 1A, 1B) according to the second aspect, the flexible external gear (3) in the first aspect is cylindrical and has an opening surface (35) on one side in the tooth trace direction (D1). The external teeth (31) protrude at least toward the opening surface (35) in the tooth trace direction (D1) relative to the internal teeth (21).

[0175] According to this embodiment, local depressions (steps) are less likely to occur on the tooth surfaces of the internal teeth (21), even at the end on the opening surface (35) side in the tooth trace direction (D1), where stress concentration due to deformation of the external teeth (31) is particularly likely to occur.

[0176] In the wave gear device (1, 1A, 1B) according to the third aspect, in the first or second aspect, at least one of the internal teeth (21) and the external teeth (31) has a tooth trace modification portion (210, 310).

[0177] According to this embodiment, stress concentration due to excessive tooth contact between the internal teeth (21) and the external teeth (31) can be prevented from occurring.

[0178] In the wave gear device (1, 1A, 1B) according to the fourth aspect, in the third aspect, the tooth trace modification portion (210) is provided on at least the internal teeth (21).

[0179] According to this aspect, tooth trace modification is not required for the flexible external gear (3) or the amount of modification can be reduced, making it easier to suppress a decrease in strength of the flexible external gear (3) due to tooth trace modification being performed on the flexible external gear (3).

[0180] In the wave gear device (1, 1A, 1B) according to the fifth aspect, in the third or fourth aspect, the internal tooth (21) has a tooth trace modification portion (210) at least at one end of the internal tooth (21) in the tooth trace direction (D1).

[0181] According to this embodiment, stress concentration due to deformation of the external teeth (31) is likely to occur at least at one end of the internal teeth (21) in the tooth trace direction (D1), but the tooth trace adjustment portion (210) makes it difficult for such stress concentration to occur.

[0182] In the wave gear device (1, 1A, 1B) according to the sixth aspect, in any one of the first to fifth aspects, the difference between the surface hardness of the internal teeth (21) and the surface hardness of the external teeth (31) is HV50 or more.

[0183] According to this embodiment, in the early stages of use of the wave gear device 1, the tooth surfaces of the internal teeth (21), which have a relatively low surface hardness, wear moderately, which increases the true contact area between the internal teeth (21) and the external teeth (31) and reduces the surface pressure, making it difficult for the external teeth (31) to wear.

[0184] In the wave gear device (1, 1A, 1B) according to the seventh aspect, in any one of the first to sixth aspects, the surface hardness of the internal teeth (21) is HV350 or less.

[0185] According to this aspect, even if foreign matter (X1) is generated due to chipping or wear of the internal teeth (21) caused by contact between the internal teeth (21) and the external teeth (31), this foreign matter (X1) is relatively soft. Therefore, by making the foreign matter (X1) generated due to wear, which is likely to be generated in the early stages of use of the wave gear device (1, 1A, 1B), soft, the amount of hard foreign matter (X1) generated that would cause significant damage to the wave gear device (1, 1A, 1B) can be reduced.

[0186] An actuator (100) according to an eighth aspect includes the strain wave gear device (1, 1A, 1B) according to any one of the first to seventh aspects, 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.

[0187] According to this aspect, foreign matter (X1) is less likely to be generated due to chipping or wear caused by contact between the internal teeth (21) and the external teeth (31), making it possible to provide an actuator (100) that is less likely to experience a decrease in reliability.

[0188] The configurations according to the second to seventh aspects are not essential for the strain wave gear device (1, 1A, 1B) and can be omitted as appropriate. [Explanation of symbols]

[0189] 1,1A,1B Strain wave gear device 2 Rigid internal gear 3 Flexible external gear 4. Wave Generator 21 Inner teeth 31 Outer teeth 35 Opening surface 100 Actuators 101 Power Source 102 Output section 210 Tooth line modification part (1st modification part) 212 Root of tooth 213 Tooth tip 310 Tooth line modification part (2nd modification part) Ax1 Rotation axis D1 tooth trace direction

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 disposed inside the flexible external gear and causing the flexible external gear to deflect, a wave gear device in which the flexible external gear is deformed in accordance with rotation of the wave generator about a rotation axis, 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 rigid internal gear and the flexible external gear, the surface hardness of the inner teeth is lower than the surface hardness of the outer teeth; The external teeth protrude in at least one direction of the tooth trace relative to the internal teeth, the flexible external gear is cup-shaped or top hat-shaped with an opening on one side in the tooth trace direction, the outer teeth protrude toward at least the opening surface side in the tooth trace direction relative to the inner teeth, a protrusion amount of the external teeth relative to the internal teeth in the tooth trace direction is greater on the opening surface side than on the opposite side of the opening surface; Wave gearing.

2. At least one of the internal teeth and the external teeth has a tooth lead modification portion. The strain wave gear device according to claim 1 .

3. The tooth lead modification portion is provided on at least the internal tooth. The strain wave gear device according to claim 2.

4. The internal tooth has the tooth trace modification portion at at least one end of the internal tooth in the tooth trace direction. The strain wave gear device according to claim 2 or 3.

5. The difference between the surface hardness of the inner teeth and the surface hardness of the outer teeth is HV50 or more. The wave gear device according to any one of claims 1 to 4.

6. The surface hardness of the internal teeth is HV350 or less. The wave gear device according to any one of claims 1 to 5.

7. The wave gear device according to any one of claims 1 to 6, a drive source that rotates the wave generator; an output unit that extracts a rotational force of either the rigid internal gear or the flexible external gear as an output. Actuator.

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