Harmonic drive gear systems, robot joint systems, and gear components

Abstract

To provide a wave gear device in which deterioration of reliability is less likely to occur, a joint device for a robot and a gear component.SOLUTION: A wave gear device 1 comprises a rigid internal gear 2, a flexible external gear 3, and a wave generator. The wave generator has a non-circular cam that is rotationally driven around a rotational shaft, and a bearing 42 that is mounted to the outside of the cam. The wave gear device 1 deforms the flexible external gear 3 as the cam rotates, engages some of external teeth 31 with some of internal teeth 21, and rotates the flexible external gear 3 relatively to the rigid internal gear 2 according to the difference in the number of teeth between the flexible external gear and the rigid internal gear 2. A portion facing an outer ring 421 of the bearing 42 on an inner peripheral surface 301 of the flexible external gear 3 comprises a small diameter part 305 that is narrower than the outer ring 421 in a tooth trace direction D1 of the external teeth 31, and a large diameter part 306 having a larger diameter than the small diameter part 305. The outer ring 421 has higher hardness than the inner peripheral surface 301 of the flexible external gear 3.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses performing surface treatment of a flexible external gear in a harmonic gear device (flexure engagement type gear device) by nitriding treatment.

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

[0004] When the wave generator rotates by a motor or the like, the meshing position of the two gears moves in the circumferential direction, and a relative rotation corresponding to the tooth number difference (2N, where N is a positive integer) between the internal teeth and the external teeth occurs between the two gears. Here, when the side of the rigid internal gear is fixed, a rotation output that is significantly decelerated according to the tooth number difference between the two gears can be obtained from the side of the flexible external gear.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the harmonic drive gear system described above, the wave generator fitted inside the flexible external gear rotates, and especially with long-term use, wear may occur at the contact points between the wave generator's bearing and the outer ring on the inner surface of the flexible external gear. This wear may cause steps to form on the inner surface of the flexible external gear at the ends (corners) of the outer ring in the width direction. When such steps are present, the outer ring repeatedly collides with these steps as the flexible external gear deforms (bends), which can lead to damage to the flexible external gear or the wave generator (bearing), potentially affecting the reliability of the harmonic drive gear system.

[0007] This disclosure is made in view of the above-mentioned reasons and aims to provide a wave drive gear device, a robot joint device, and gear components that are less prone to a decrease in reliability. [Means for solving the problem]

[0008] A harmonic drive gear according to one aspect of the present disclosure comprises 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 positioned inside the rigid internal gear. The wave generator has a non-circular cam that is rotationally driven around a rotation axis, and a bearing mounted on the outside of the cam. The wave generator is positioned inside the flexible external gear and causes the flexible external gear to bend. The harmonic drive gear deforms the flexible external gear as the cam rotates, engaging a portion of the external teeth with a portion of the internal teeth, and causing the flexible external gear to rotate relative to the rigid internal gear in proportion to the difference in the number of teeth between the two gears. The portion of the inner circumferential surface of the flexible external gear facing the outer ring of the bearing includes a small-diameter portion that is narrower than the outer ring in the tooth trace direction of the external teeth, and a large-diameter portion that is larger in diameter than the small-diameter portion. The outer ring has higher hardness compared to the inner circumferential surface of the flexible external gear.

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

[0010] A gear component according to one aspect of this disclosure is used as the flexible external gear of the harmonic drive gear. [Effects of the Invention]

[0011] According to this disclosure, there is an advantage in that we can provide wave drive gears, robot joints, and gear components that are less prone to reliability degradation. [Brief explanation of the drawing]

[0012] [Figure 1A] Figure 1A is a cross-sectional view showing the schematic configuration of a harmonic drive gear according to Embodiment 1. [Figure 1B] Figure 1B is an enlarged view of region Z1 in Figure 1A. [Figure 2A] Figure 2A is a schematic diagram of the same harmonic drive gear as seen from the input side of the rotating shaft. [Figure 2B] Figure 2B is an enlarged view of region Z1 in Figure 2A. [Figure 3A] Figure 3A is a schematic exploded perspective view of the same harmonic drive gear as shown above, viewed from the output side of the rotating shaft. [Figure 3B] Figure 3B is a schematic exploded perspective view of the same harmonic drive gear as seen from the input side of the rotating shaft. [Figure 4] Figure 4 is a cross-sectional view showing the schematic configuration of the actuator, including the harmonic drive gear shown above. [Figure 5] Figure 5 is a schematic cross-sectional view showing an enlarged view of the main parts of the area corresponding to Figure 1B. [Figure 6] Figure 6 is a schematic diagram showing an enlarged view of region Z1 in Figure 5. [Figure 7] Figure 7 is a conceptual diagram illustrating the operation of the long axis and short axis sides of the tapered surface of the harmonic drive gear shown above. [Figure 8] Figure 8 is a cross-sectional view showing an example of a robot using the same harmonic drive gear system. [Figure 9] FIG. 9 is a schematic cross-sectional view showing an enlarged main part of a range corresponding to FIG. 1B in the harmonic gear device according to Embodiment 2.

MODE FOR CARRYING OUT THE INVENTION

[0013] (Embodiment 1) (1) Overview Hereinafter, the overview of the harmonic gear device 1 according to the present embodiment will be described with reference to FIGS. 1A to 5. The drawings referred to in the present disclosure are all schematic drawings, and the ratios of the sizes and thicknesses of each component in the drawings do not necessarily reflect the actual dimensional ratios. For example, the tooth profiles, dimensions, number of teeth, etc. of the internal teeth 21 and external teeth 31 in FIGS. 2A to 3B are only schematically shown for the purpose of explanation, and are not intended to be limited to the illustrated shapes.

[0014] The harmonic gear device 1 according to the present embodiment is a gear device including a rigid internal gear 2, a flexible external gear 3, and a wave generator 4. In this harmonic gear device 1, an annular flexible external gear 3 is disposed inside an annular rigid internal gear 2, and further, a wave generator 4 is disposed inside the flexible external gear 3. The wave generator 4 partially meshes the external teeth 31 of the flexible external gear 3 with the internal teeth 21 of the rigid internal gear 2 by bending the flexible external gear 3 into a non-circular shape. 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 tooth number difference between the rigid internal gear 2 and the flexible external gear 3 occurs between the two gears (the rigid internal gear 2 and the flexible external gear 3). Here, if the rigid internal gear 2 is fixed, the flexible external gear 3 rotates as the relative rotation of the two gears occurs. As a result, a rotational output decelerated at a relatively high reduction ratio can be obtained from the flexible external gear 3 according to the tooth number difference between the two gears.

[0015] Further, the wave generator 4 that causes the flexible external gear 3 to flex has a non-circular cam 41 that is rotationally driven about the input-side rotation axis Ax1 (see FIG. 1A) and a bearing 42. The bearing 42 is disposed between the outer peripheral surface 411 of the cam 41 and the inner peripheral surface 301 of the flexible external gear 3. The 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 elastically deformed by being pressed by the cam 41 via the ball-shaped rolling elements 423. Here, since the outer ring 421 can rotate relative to the inner ring 422 as the rolling elements 423 roll, 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 occurs in the external teeth 31 of the flexible external gear 3 that is pressed by the cam 41. When the wave motion of the external teeth 31 occurs, as described above, 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 relative rotation occurs between the flexible external gear 3 and the rigid internal gear 2.

[0016] In short, in this type of harmonic gear device 1, the wave generator 4 having the bearing 42 flexes the flexible external gear 3 while realizing power transmission by the meshing of the internal teeth 21 and the external teeth 31.

[0017] In this type of harmonic gear device 1, particularly, after long-term use, with the rotation of the wave generator 4 fitted inside the flexible external gear 3, wear may occur at the contact portion between the outer ring 421 of the bearing 42 of the wave generator 4 and the inner peripheral surface 301 of the flexible external gear 3. Due to this wear, a step may occur at the portions corresponding to both ends (corners) in the width direction (rotation axis Ax1 direction) of the outer ring 421 on the inner peripheral surface 301 of the flexible external gear 3. In a state where such a step has occurred, as the flexible external gear 3 deforms (flexes), the outer ring 421 repeatedly collides with the step, which may lead to damage to the flexible external gear 3 or the wave generator 4 (bearing 42 thereof), and may affect the reliability of the harmonic gear device 1.

[0018] In other words, the outer ring 421 of the bearing 42 of the wave generator 4 is within the range of the flexible external gear 3 in a direction parallel to the rotation axis Ax1. Here, for example, in a wave drive gear device 1 in which the wave generator 4 causes the flexible external gear 3 to bend into an elliptical shape, the flexible external gear 3 undergoes elastic deformation twice in one direction (for example, the vertical direction in Figure 2A) where the major axis of the ellipse is in one direction during one rotation of the cam 41 of the wave generator 4. Therefore, as the cam 41 rotates at high speed, the flexible external gear 3 undergoes repeated elastic deformation at high speed, and vibrations are likely to occur at the contact point between the flexible external gear 3 and the wave generator 4 due to these repeated elastic deformations. As a result of such vibrations, both ends (corners) in the width direction of the outer ring 421 are repeatedly pressed against the inner circumferential surface 301 of the flexible external gear 3, and the parts where both ends in the width direction of the outer ring 421 make contact are more prone to wear than other parts. Furthermore, the inner circumferential surface 301 of the flexible external gear 3 may have lower hardness than the outer ring 421 of the bearing 42. In such cases, wear is more likely to occur on the inner circumferential surface 301 of the flexible external gear 3 where the outer ring 421 contacts both ends in the width direction.

[0019] As a result, on the inner circumferential surface 301 of the flexible external gear 3, the areas where the outer ring 421 contacts the inner circumferential surface 301 in the width direction may wear locally (significantly more than other areas), potentially creating a "step" between these areas and the areas where the outer ring 421 does not make contact. In other words, a pair of steps spaced apart in the thrust direction (parallel to the rotation axis Ax1) may occur on the inner circumferential surface 301 of the flexible external gear 3, and the outer ring 421 will be sandwiched between these steps. In this state, each time the cam 41 of the wave generator 4 rotates and the flexible external gear 3 deforms (bends), a thrust load is applied to the steps from the outer ring 421. Consequently, this can lead to deterioration or damage to the flexible external gear 3 or the wave generator 4 (bearing 42), resulting in a decrease in the reliability of the wave gear unit 1. Therefore, the harmonic drive gear 1 according to this embodiment suppresses the occurrence of steps on the inner circumferential surface 301 of the flexible external gear 3 by the following configuration, thereby reducing the likelihood of a decrease in reliability.

[0020] In other words, as shown in Figures 1A to 3B, the harmonic drive gear 1 according to this embodiment comprises 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 positioned inside the rigid internal gear 2. The wave generator 4 is positioned inside the flexible external gear 3 and causes the flexible external gear 3 to bend. The wave generator 4 has a non-circular cam 41 that is rotationally driven around a rotation axis Ax1, and a bearing 42 mounted on the outside of the cam 41. The harmonic drive gear 1 deforms the flexible external gear 3 as the cam 41 rotates, engaging a portion of the external teeth 31 with a portion of the internal teeth 21, and causing the flexible external gear 3 to rotate relative to the rigid internal gear 2 according to the difference in the number of teeth between it and the rigid internal gear 2. Here, as shown in Figure 5, the portion of the bearing 42 facing the outer ring 421 on the inner circumferential surface 301 of the flexible external gear 3 includes a small-diameter portion 305 that is narrower than the outer ring 421 in the tooth trace direction D1 of the external teeth 31, and a large-diameter portion 306 that is larger in diameter than the small-diameter portion 305.

[0021] In this embodiment, the inner circumferential surface 301 of the flexible external gear 3 contacts the outer ring 421 only at the small diameter portion 305 of the bearing 42 facing the outer ring 421, and does not contact the outer ring 421 at the large diameter portion 306. Furthermore, the small diameter portion 305 of the inner circumferential surface 301 of the flexible external gear 3, which is the contact portion with the outer ring 421, is narrower than the outer ring 421 in the tooth trace direction D1 of the external teeth 31. Therefore, the outer ring 421 is less likely to come into contact with the inner circumferential surface 301 of the flexible external gear 3 at both ends (corners) in the width direction, and the outer ring 421 makes surface contact with the small diameter portion 305, which is the contact portion with the outer ring 421. Consequently, the portion of the inner circumferential surface 301 of the flexible external gear 3 facing the outer ring 421 of the bearing 42 will wear uniformly over the entire small diameter portion 305 that the outer ring 421 contacts.

[0022] As a result, the inner circumferential surface 301 of the flexible external gear 3 is less prone to "steps" caused by localized wear (larger than other areas) at the points where the outer ring 421 contacts the gear in the width direction. Therefore, in the harmonic drive gear 1 according to this embodiment, steps are less likely to occur on the inner circumferential surface 301 of the flexible external gear 3 due to contact with the bearing 42 (outer ring 421), making it possible to provide a harmonic drive gear 1 that is less prone to a decrease in reliability. Furthermore, since the harmonic drive gear 1 according to this embodiment is less prone to a decrease in reliability, especially during long-term use, it leads to improved transmission efficiency, longer lifespan, and higher performance of the harmonic drive gear 1.

[0023] Furthermore, as shown in Figure 4, the harmonic drive gear 1 according to this embodiment, together with the drive source 101 and the output unit 102, constitutes the actuator 100. In other words, the actuator 100 according to this embodiment comprises the harmonic drive gear 1, the drive source 101, and the 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.

[0024] Furthermore, as shown in Figure 4, the harmonic drive gear 1 according to this embodiment, together with the first member 131 and the second member 132, constitutes a robot joint device 130. In other words, the robot joint device 130 according to this embodiment comprises the harmonic drive gear 1, the first member 131, and the second member 132. The first member 131 is fixed to the rigid internal gear 2. The second member 132 is fixed to the flexible external gear 3. As a result, relative rotation occurs between the flexible external gear 3 and the rigid internal gear 2 in the harmonic drive gear 1, causing the first member 131 and the second member 132 in the robot joint device 130 to rotate relative to each other.

[0025] The robot joint device 130 according to this embodiment has the advantage that it is less likely to cause a decrease in the reliability of the wave gear device 1.

[0026] (2) Definition In this disclosure, "annular" means a ring-like shape that forms an enclosed space (region) at least in a plan view, and is not limited to a circular shape (annular) that is a perfect circle in a plan view, but may also be an elliptical shape, a polygonal shape, etc. Furthermore, even if the shape has a bottom portion 322, such as a cup-shaped flexible external gear 3, if its body portion 321 is annular, it is called an "annular" flexible external gear 3.

[0027] In this disclosure, "rigidity" refers to the property of an object to resist deformation when an external force is applied to it. In other words, a rigid object is difficult to deform even when an external force is applied. On the other hand, 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, a flexible object is easily elastically deformed when an external force is applied to it. Therefore, "rigidity" and "flexibility" have opposite meanings.

[0028] In particular, in this disclosure, the terms "rigidity" of the rigid internal gear 2 and "flexibility" of the flexible external gear 3 are used in a relative sense. That is, the "rigidity" of the rigid internal gear 2 means that, at least relatively compared to the flexible external gear 3, the rigid internal gear 2 has high rigidity, meaning it is less likely to deform even when an external force is applied. Similarly, the "flexibility" of the flexible external gear 3 means that, at least relatively compared to the rigid internal gear 2, the flexible external gear 3 has high flexibility, meaning it is more easily elastically deformed when an external force is applied.

[0029] Furthermore, in this disclosure, one side of the rotating shaft Ax1 (the right side in Figure 1A) may be referred to as the "input side," and the other side of the rotating shaft Ax1 (the left side in Figure 1A) may be referred to as the "output side." In other words, in the example in Figure 1A, the flexible external gear 3 has an opening surface 35 on the "input side" of the rotating shaft Ax1. However, the terms "input side" and "output side" are merely labels used for explanatory purposes and are not intended to limit the positional relationship between the input and output as viewed from the harmonic drive gear 1.

[0030] In this disclosure, "non-circular shape" means a shape that is not a perfect circle, and includes, for example, elliptical and oblong shapes. In this embodiment, as an example, the non-circular cam 41 of the wave generator 4 is elliptical in shape. In other words, in this embodiment, the wave generator 4 causes the flexible external gear 3 to bend into an elliptical shape.

[0031] In this disclosure, "elliptical shape" refers to any shape in which a perfect circle is compressed, with the intersection of mutually orthogonal major and minor axes located at the center, and is not limited to a mathematical "ellipse," which is a curve consisting of 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 curve consisting of 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 oblong. As mentioned above, the drawings referenced in this disclosure are all schematic diagrams, and the ratios of the size and thickness of each component in the drawings do not necessarily reflect the actual dimensional ratios. For example, in Figure 2A, the shape of the cam 41 of the wave generator 4 is shown as a somewhat exaggerated elliptical shape, but this is not intended to limit the actual shape of the cam 41.

[0032] In this disclosure, "axis of rotation" refers to a hypothetical axis (straight line) that is the center of the rotational motion of the rotating body. In other words, axis of rotation Ax1 is a hypothetical axis without physical existence. The wave generator 4 performs rotational motion around axis of rotation Ax1.

[0033] In this disclosure, "internal teeth" and "external teeth" refer not to individual "teeth," but to a collection (group) of multiple "teeth." In other words, the internal teeth 21 of the rigid internal gear 2 consist of a collection 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 consist of a collection of multiple teeth formed on the outer circumferential surface of the flexible external gear 3.

[0034] In this disclosure, "parallel" means that two lines on a single plane will never intersect no matter how far they are extended, meaning the angle between them is exactly 0 degrees (or 180 degrees), and also that the angle between them falls within an error range of a few degrees (for example, less than 10 degrees) relative to 0 degrees. Similarly, in this disclosure, "orthogonal" means that two lines intersect at an angle of exactly 90 degrees, and also that the angle between them falls within an error range of a few degrees (for example, less than 10 degrees) relative to 90 degrees.

[0035] (3) Composition The detailed configurations of the wave gear device 1, actuator 100, and robot joint device 130 according to this embodiment will be described below with reference to Figures 1A to 4.

[0036] Figure 1A is a cross-sectional view showing the schematic configuration of the harmonic drive gear 1, and Figure 1B is an enlarged view of region Z1 in Figure 1A. Figure 2A is a schematic view of the harmonic drive gear 1 as seen from the input side of the rotating shaft Ax1 (right side in Figure 1A), and Figure 2B is an enlarged view of region Z1 in Figure 2A. Figure 3A is a schematic exploded perspective view of the harmonic drive gear 1 as seen from the output side of the rotating shaft Ax1 (left side in Figure 1A). Figure 3B is a schematic exploded perspective view of the harmonic drive gear 1 as seen from the input side of the rotating shaft Ax1. Figure 4 is a cross-sectional view showing the schematic configuration of the actuator 100 and the robot joint device 130, including the harmonic drive gear 1.

[0037] (3.1) Harmonic drive gear As described above, the harmonic drive gear 1 according to this embodiment comprises a rigid internal gear 2, a flexible external gear 3, and a 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 harmonic drive gear 1, are metals such as stainless steel, cast iron, carbon steel for machine structures, chromium-molybdenum steel, phosphor bronze, or aluminum bronze. The term "metal" here includes metals that have undergone surface treatment such as nitriding.

[0038] Furthermore, in this embodiment, a cup-shaped harmonic drive gear is given as an example of the harmonic drive gear 1. That is, the harmonic drive gear 1 according to this embodiment uses a cup-shaped flexible external gear 3. 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] Furthermore, in this embodiment, as an example, the wave drive gear 1 is used with the rigid internal gear 2 fixed to the input-side case 111 (see Figure 4) and the output-side case 112 (see Figure 4), etc. As a result, the flexible external gear 3 rotates relative to the fixed member (input-side case 111, etc.) as the rigid internal gear 2 and the flexible external gear 3 rotate relative to each other.

[0040] Furthermore, in this embodiment, when the harmonic drive gear 1 is used as the actuator 100, a rotational force is applied to the wave generator 4 as input, and a rotational force is extracted as output from the flexible external gear 3. In other words, the harmonic drive gear 1 operates using 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 harmonic drive gear 1 obtains an output rotation that is reduced at a relatively high reduction ratio relative to the input rotation.

[0041] Furthermore, in the harmonic drive gear 1 according to this embodiment, the input rotation axis Ax1 and the output rotation axis Ax2 are on the same straight line. In other words, the input rotation axis Ax1 and the output rotation axis Ax2 are coaxial. Here, the input rotation axis Ax1 is the rotation center of the wave generator 4 to which the input rotation is applied, and the output rotation axis Ax1 is the rotation center of the flexible external gear 3 that generates the output rotation. In other words, in the harmonic drive gear 1, an output rotation reduced at a relatively high reduction ratio relative to the input rotation is obtained on the same axis.

[0042] The rigid internal gear 2, also known as a circular spline, is an annular component having internal teeth 21. In this embodiment, the rigid internal gear 2 has an annular shape, with at least its inner circumferential surface being a perfect circle in 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. All of the teeth constituting the internal teeth 21 are of the same shape and are provided at equal pitches 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 plan view. The rigid internal gear 2 also has a predetermined thickness in the direction of the rotation axis Ax1. All of the internal teeth 21 are formed along the entire length in the thickness direction of the rigid internal gear 2. The tooth traces of the internal teeth 21 are all parallel to the rotation axis Ax1.

[0043] As described above, the rigid internal gear 2 is fixed to the input case 111 (see Figure 4) and the output case 112 (see Figure 4), etc. Therefore, the rigid internal gear 2 has multiple fixing holes 22 (see Figures 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 in a cup shape from a relatively thin-walled metallic elastic body (metal plate). In other words, the flexible external gear 3 is flexible because of its relatively small thickness (thinness). The flexible external gear 3 has a cup-shaped main body 32. The main body 32 has a body portion 321 and a bottom portion 322. The body portion 321 has a cylindrical shape such that at least its inner circumferential surface 301 is a perfect circle in plan view when the flexible external gear 3 is not elastically deformed. The central axis of the body portion 321 coincides with the rotation axis Ax1. The bottom portion 322 is located on one of the opening surfaces of the body portion 321 and has a disc shape that is a perfect circle in plan view. The bottom portion 322 is positioned on the output side of the rotation axis Ax1 of the pair of opening surfaces of the body portion 321. As described above, the main body portion 32, as a whole, including the body portion 321 and the bottom portion 322, has a bottomed cylindrical, or cup-shaped, form that is open to the input side of the rotation axis Ax1. In other words, an opening surface 35 is formed on the end face of the flexible external gear 3 opposite to the bottom portion 322 in the direction of the rotation axis Ax1. That is, the flexible external gear 3 is cylindrical with an opening surface 35 on one side of the tooth trace direction D1 (in this case, the input side of the rotation axis Ax1). In this embodiment, the body portion 321 and the bottom portion 322 are integrally formed from a single metal member, thereby realizing a seamless main body portion 32.

[0045] In this configuration, the wave generator 4 is fitted into the inside of the body 321 of the flexible external gear 3, thereby combining it with the flexible external gear 3. 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 out, causing it to elastically deform in a non-circular shape. In this embodiment, the combination of the wave generator 4 with the flexible external gear 3 causes the body 321 of the flexible external gear 3 to elastically deform into an elliptical shape. In other words, a state in which elastic deformation does not occur in the flexible external gear 3 means that 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 that the wave generator 4 is combined with the flexible external gear 3.

[0046] More specifically, the wave generator 4 is fitted into the inner circumferential surface 301 of the body 321 on the side opposite to the bottom 322 (the input side of the rotation axis Ax1). In other words, the wave generator 4 is fitted into the end of the body 321 of the flexible external gear 3 on the side of the opening surface 35 in the direction of the rotation axis Ax1. Therefore, when the flexible external gear 3 is undergoing elastic deformation, the flexible external gear 3 deforms more significantly at the end on the opening surface 35 in the direction of the rotation axis Ax1 compared to the end on the bottom 322 side, resulting in a shape closer to an ellipse. Due to this difference in the amount of deformation in the direction of the rotation axis Ax1, when the flexible external gear 3 is undergoing elastic deformation, the inner circumferential surface 301 of the body 321 of the flexible external gear 3 includes a tapered surface 302 (see Figure 7) that is inclined with respect to the rotation axis Ax1.

[0047] Furthermore, 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 to 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 on the side of the opening surface 35 in the direction of the rotation axis Ax1. All of the teeth constituting the external teeth 31 are of the same shape and are provided at equal pitches over the entire circumferential area of ​​the outer circumferential surface of the flexible external gear 3. That is, the pitch circle of the external teeth 31 is a perfect circle in plan view when no elastic deformation occurs in the flexible external gear 3. The external teeth 31 are formed only within a certain width range from the edge of the body portion 321 on the side of the opening surface 35 (the input side of the rotation axis Ax1). Specifically, in the body portion 321, at least the portion into which the wave generator 4 is fitted (the end on the side of the opening surface 35) in the direction of the rotation axis Ax1 has external teeth 31 formed on its outer surface. The tooth traces of the external teeth 31 are all parallel to the rotation axis Ax1.

[0048] In short, in the harmonic drive gear 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 the direction parallel to the rotation axis Ax1. Furthermore, since the dimension of the tooth trace direction D1 in the internal teeth 21 is the tooth width of the internal teeth 21, and similarly, the dimension of the tooth trace direction D1 in the external teeth 31 is the tooth width of the external teeth 31, the tooth trace direction D1 is synonymous with the tooth width direction.

[0049] In this embodiment, as described above, the rotation of the flexible external gear 3 is extracted as output rotation. Therefore, the output unit 102 (see Figure 4) of the actuator 100 is attached to the flexible external gear 3. Multiple mounting holes 33 are formed in the bottom portion 322 of the flexible external gear 3 for attaching the shaft that serves as the output unit 102. Furthermore, a through hole 34 is formed in the center of the bottom portion 322. The area around the through hole 34 in the bottom portion 322 is thicker than other parts of the bottom portion 322.

[0050] The flexible external gear 3, configured in this way, is positioned inside the rigid internal gear 2. Here, the flexible external gear 3 is combined with the rigid internal gear 2 such that only the end of the outer circumferential surface of the body 321 opposite to the bottom 322 (the input side of the rotation axis Ax1) is inserted inside the rigid internal gear 2. In other words, of the body 321, the portion where the wave generator 4 is fitted (the end on the opening surface 35 side) in the direction of the rotation axis Ax1 is inserted inside the rigid internal gear 2. Here, external teeth 31 are formed on the outer circumferential surface 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 positioned 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 in the rigid internal gear 2 is 2N (where N is a positive integer) greater than the number of teeth of the external teeth 31 in the flexible external gear 3. In this embodiment, as an example, N is "1", and the number of teeth (external teeth 31) of the flexible external gear 3 is "2" greater than the number of teeth (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 harmonic drive gear 1.

[0052] In this embodiment, as an example, as shown in Figures 1A and 1B, 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 such that the center of the tooth trace direction D1 of the external teeth 31 and the center of the tooth trace direction D1 of the internal teeth 21 face each other. In other words, the positions of the centers of the tooth trace direction D1 of the external teeth 31 of the flexible external gear 3 and the internal teeth 21 of the rigid internal gear 2 are aligned to the same position in the direction of the rotation axis Ax1. Furthermore, 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 will be contained within the range of the tooth trace of the external teeth 31. In other words, the external teeth 31 protrude from the internal teeth 21 in at least one direction in the tooth trace direction D1. In this embodiment, the external teeth 31 protrude from the internal teeth 21 in both directions of the tooth trace direction D1 (input side and output side of the rotation axis Ax1).

[0053] Here, in a state where no elastic deformation occurs in the flexible external gear 3 (a state where the wave generator 4 is not combined with the flexible external gear 3), the pitch circle of the circular external teeth 31 is set to be slightly smaller than the pitch circle of the circular internal teeth 21. 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 in between, and do not mesh with each other.

[0054] On the other hand, when the flexible external gear 3 undergoes elastic deformation (when the wave generator 4 is combined with the flexible external gear 3), the body 321 bends in an elliptical (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, as the body 321 of the flexible external gear 3 (at least the end on the side of the opening surface 35) elastically deforms into an elliptical shape, the external teeth 31 located at both ends along the long axis of the ellipse mesh with the internal teeth 21, as shown in Figure 2A. To put it another way, the major axis of the pitch circle of the elliptical external teeth 31 coincides with the diameter of the pitch circle of the circular internal teeth 21, and the minor axis of the pitch circle of the elliptical external teeth 31 is smaller than the diameter of the pitch circle of the circular internal teeth 21. In this way, when the flexible external gear 3 undergoes elastic deformation, some of the teeth that make up the external gear 31 mesh with some of the teeth that make up the internal gear 21. As a result, the harmonic drive gear 1 makes it possible to mesh some of the external gears 31 with some of the internal gears 21.

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

[0056] The wave generator 4 has a non-circular (elliptical in this case) cam 41 and a bearing 42 mounted on the outer circumference of the cam 41. In other words, the cam 41 is fitted into the bearing 42 so that it fits inside the inner ring 422 of the bearing 42. As a result, the bearing 42 receives an external force from the cam 41 in the radial direction (direction perpendicular to the rotation axis Ax1) from the inside to the outside of the inner ring 422, causing it to elastically deform in a non-circular shape. In other words, a state in which no elastic deformation occurs in the bearing 42 means that the cam 41 is not assembled to the bearing 42. Conversely, a state in which elastic deformation occurs in the bearing 42 means that the cam 41 is assembled to the bearing 42.

[0057] The cam 41 is a non-circular (in this case, elliptical) component that is rotationally driven around the input rotation axis Ax1. The cam 41 has an outer circumferential surface 411 (see Figure 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). As a result, the cam 41 has a rigidity similar to that of the rigid internal gear 2. However, the thickness of the cam 41 is smaller (thinner) than that of the rigid internal gear 2. In this embodiment, as described above, the rotation of the wave generator 4 is used as the input rotation. Therefore, the input part 103 (see Figure 4) of the actuator 100 is attached to the wave generator 4. A cam hole 43 for attaching the shaft that serves as the input part 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 spherical balls as the rolling elements 423.

[0059] Both the outer ring 421 and the inner ring 422 are annular components. Both the outer ring 421 and the inner ring 422 are annular components formed from relatively thin-walled metallic elastic material (metal plate). In other words, each of the outer ring 421 and the inner ring 422 is flexible due to its relatively small thickness (thinness). In this embodiment, both the outer ring 421 and the inner ring 422 have annular shapes that are perfectly round in plan view when the bearing 42 is not elastically deformed (when the cam 41 is not assembled to the bearing 42). The inner ring 422 is slightly smaller than the outer ring 421 and is positioned inside the outer ring 421. Here, since the inner diameter of the outer ring 421 is larger than the outer diameter of the inner ring 422, a gap is created between the inner circumferential surface 425 of the outer ring 421 and the outer circumferential surface of the inner ring 422.

[0060] Multiple rolling elements 423 are positioned in the gap between the outer ring 421 and the inner ring 422. The multiple rolling elements 423 are arranged in a line along the circumference of the outer ring 421. All of the multiple rolling elements 423 are metal balls of the same shape and are provided at equal pitches over the entire circumference of the outer ring 421. Although not specifically shown here, the bearing 42 further has a cage, and the multiple rolling elements 423 are held between the outer ring 421 and the inner ring 422 by the cage.

[0061] Furthermore, in this embodiment, as an example, the widthwise dimensions (parallel to the rotation axis Ax1) of the outer ring 421 and inner ring 422 are the same as the thickness of the cam 41. In other words, the widthwise dimensions of the outer ring 421 and inner ring 422 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 to 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 conforms to the outer circumference 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 (with the cam 41 assembled to the bearing 42), the outer ring 421 and the inner ring 422 form elliptical shapes that are similar to each other.

[0063] Even when the bearing 42 is elastically deformed, the gap between the outer ring 421 and the inner ring 422 is kept approximately constant around the entire circumference of the outer ring 421 because of the multiple rolling elements 423 interposed between them. In this state, the multiple rolling elements 423 between the outer ring 421 and the inner ring 422 roll, allowing the outer ring 421 to rotate relative to the inner ring 422. Therefore, when the cam 41 rotates around the rotation axis Ax1 while the bearing 42 is elastically deformed, 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 around the rotation axis Ax1, the outer ring 421 elastically deforms so that the major axis of the elliptical shape formed by the outer ring 421 rotates around the rotation axis Ax1. Therefore, the overall shape of the wave generator 4, as viewed from the input side of the rotation axis Ax1, is elliptical, and its outer circumference changes as the cam 41 rotates, such that its major axis rotates around the rotation axis Ax1.

[0064] The wave generator 4, configured in this way, is positioned inside the flexible external gear 3. Here, the flexible external gear 3 is assembled with the wave generator 4 such that only the end of the inner circumferential surface 301 of the body portion 321 opposite to the bottom portion 322 (the side with the opening surface 35) is fitted into the wave generator 4. At this time, the bearing 42 of the wave generator 4 is positioned between the outer circumferential surface 411 of the cam 41 and the inner circumferential surface 301 of the flexible external gear 3. Here, the outer diameter of the outer ring 421 when no elastic deformation occurs in the bearing 42 (when the cam 41 is not assembled to the bearing 42) is the same as the inner diameter of the flexible external gear 3 (body portion 321) when no elastic deformation occurs. The inner diameter of the flexible external gear 3 referred to here is the diameter φ11 of the small diameter portion 305 on the inner circumferential surface 301 of the flexible external gear 3 (see Figure 6). Therefore, the outer circumferential surface 424 (see Figure 5) 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 circumference of the bearing 42. Thus, 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 321 will bend in an elliptical (non-circular) shape. In this state, the flexible external gear 3 is fixed to the outer ring 421 of the bearing 42.

[0065] However, since the flexible external gear 3 and the wave generator 4 are only fitted together, the flexible external gear 3 and the outer ring 421 of the bearing 42 are not completely fixed. Therefore, a small gap X1 (see Figure 1B) is created between the flexible external gear 3 and the outer ring 421 fitted inside the flexible external gear 3. More precisely, since the outer circumferential surface 424 of the outer ring 421 is slightly smaller in diameter than the inner circumferential surface 301 of the flexible external gear 3, the gap X1 between the outer ring 421 and the flexible external gear 3 is not completely filled, and at least a partial gap X1 remains. Due to the influence of this gap X1, as the cam 41 of the wave generator 4 rotates and the outer ring 421 and the flexible external gear 3 elastically deform, relative rotation may occur between the outer ring 421 and the flexible external gear 3. This relative rotation is, for example, only a fraction of a thousand or a few hundredth of the rotational speed of the cam 41, but the relative friction between the outer ring 421 and the flexible external gear 3 due to such relative rotation is one of the causes of fretting wear.

[0066] In this disclosure, "gap" refers to the space that can occur between the opposing surfaces of two objects, and a gap can occur between the two objects even if they are not separated. In other words, even if two objects are in contact, a small gap can still occur between them. Between the flexible external gear 3 and the outer ring 421 fitted inside the flexible external gear 3, a gap X1 occurs between the outer circumferential surface 424 of the outer ring 421 and the inner circumferential surface 301 of the flexible external gear 3, which are opposite each other. However, basically, the outer circumferential surface 424 of the outer ring 421 and the inner circumferential surface 301 of the flexible external gear 3 are in contact, so a large gap X1 does not occur between them. Therefore, the gap X1 between the outer ring 421 and the flexible external gear 3 is a small gap that may occur partially between the outer circumferential surface 424 of the outer ring 421 and the inner circumferential surface 301 of the flexible external gear 3. As an example, a microscopic gap X1 is created between the outer circumferential surface 424 of the outer ring 421 and the inner circumferential surface 301 of the flexible external gear 3, allowing the lubricant Lb1 to penetrate.

[0067] In the harmonic drive gear 1 with the above configuration, as shown in Figure 2A, the body 321 of the flexible external gear 3 bends in an elliptical (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 elastic deformation of the flexible external gear 3 (body 321) into an elliptical shape causes the two external teeth 31 corresponding to both ends of the long axis of that ellipse 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 the multiple rolling elements 423. Therefore, the outer circumference of the elliptical flexible external gear 3, as 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.

[0068] As a result, wave motion occurs in the external teeth 31 formed on the outer circumferential surface of the flexible external gear 3. The wave motion of 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, resulting in relative rotation between the flexible external gear 3 and the rigid internal gear 2. In other words, since the external teeth 31 mesh with the internal teeth 21 at both ends in the direction of the major axis of the elliptical shape formed by the body 321 of the flexible external gear 3, the meshing position between the internal teeth 21 and the external teeth 31 moves as the major axis of this elliptical shape rotates around the rotation axis Ax1. Thus, the wave gear device 1 according to this embodiment deforms the flexible external gear 3 in accordance with the rotation of the wave generator 4 around the rotation axis Ax1, meshing a part of the external teeth 31 with a part of the internal teeth 21, and rotating the flexible external gear 3 in accordance with the difference in the number of teeth between it and the rigid internal gear 2.

[0069] Incidentally, in the harmonic drive gear 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 harmonic drive gear 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 equation 1.

[0070] R1 = V2 / (V1 - V2) ... (Equation 1) In short, 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. For 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 from equation 1 above, the reduction ratio R1 is "35". In this case, when viewed from the input side of the rotation axis Ax1, if the cam 41 rotates clockwise one full turn (360 degrees) around the rotation axis Ax1, the flexible external gear 3 rotates counterclockwise by the amount of the difference in the number of teeth "2" (i.e., 10.3 degrees) around the rotation axis Ax1.

[0071] According to the harmonic drive gear device 1 of this embodiment, such a high reduction ratio R1 can be achieved with a single-stage gear combination (rigid internal gear 2 and flexible external gear 3).

[0072] Furthermore, the wave drive gear unit 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 as described in the section "(3.2) Actuator" as a component.

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

[0074] As shown in Figure 4, the actuator 100 according to this embodiment comprises a harmonic drive gear 1, a drive source 101, and an output unit 102. In other words, the actuator 100 comprises a drive source 101 and an output unit 102 in addition to the rigid internal gear 2, flexible external gear 3, and wave generator 4 that constitute the harmonic drive gear 1. Furthermore, the actuator 100 further comprises an input unit 103, an input-side case 111, an output-side case 112, a spline bush 113, a spacer 114, a first fastener 115, a second fastener 116, and a mounting plate 117. In this embodiment, the actuator 100 further comprises input-side bearings 118, 119, an input-side oil seal 120, output-side bearings 121, 122, and an output-side oil seal 123.

[0075] In this embodiment, the materials of the components of the actuator 100 other than the drive source 101, input side oil seal 120, and output side oil seal 123 are metals such as stainless steel, cast iron, structural carbon steel, chromium molybdenum steel, phosphor bronze, or aluminum bronze.

[0076] The drive source 101 is a power source such as a motor. The power generated by the drive source 101 is transmitted to the cam 41 of the wave generator 4 in the wave drive gear unit 1. Specifically, the drive source 101 is connected to a shaft which serves as an input section 103, and the power generated by the drive source 101 is transmitted to the cam 41 via the input section 103. This allows the drive source 101 to rotate the cam 41.

[0077] The output unit 102 is a cylindrical shaft positioned along the rotation axis Ax2 on the output side. The central axis of the shaft as the output unit 102 coincides with the rotation axis Ax2. The output unit 102 is held in the output side case 112 so that it can rotate around the rotation axis Ax2. The output unit 102 is fixed to the bottom 322 of the main body 32 of the flexible external gear 3 and rotates together with the flexible external gear 3 around the rotation axis Ax2. In other words, the output unit 102 extracts the rotational force of the flexible external gear 3 as an output.

[0078] The input unit 103 is a cylindrical shaft positioned along the input-side rotation axis Ax1. The central axis of the shaft as the input unit 103 coincides with the rotation axis Ax1. The input unit 103 is held in the input-side case 111 so that it can rotate 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 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, so the input unit 103 and the output unit 102 are located coaxially.

[0079] The input-side case 111 holds the input section 103 via input-side bearings 118 and 119 so that the input section 103 can rotate. The pair of input-side bearings 118 and 119 are arranged side by side with a gap between them along the rotation axis Ax1. In this embodiment, the shaft, which is the input section 103, passes through the input-side case 111, and the tip of the input section 103 protrudes from the input-side end face of the rotation axis Ax1 in the input-side case 111 (the right end face in Figure 4). The gap between the input section 103 and the input-side end face of the rotation axis Ax1 in the input-side case 111 is sealed by the input-side oil seal 120.

[0080] The output case 112 holds the output unit 102 via output bearings 121 and 122 so that the output unit 102 can rotate. The pair of output bearings 121 and 122 are arranged side by side with a gap between them along the rotation axis Ax2. In this embodiment, the shaft, which is the output unit 102, passes through the output case 112, and the tip of the output unit 102 protrudes from the output-side end face of the rotation axis Ax1 in the output case 112 (the left end face in Figure 4). The gap between the output unit 102 and the output-side end face of the rotation axis Ax1 in the output case 112 is sealed by the output oil seal 123.

[0081] Here, as shown in Figure 4, the input case 111 and the output case 112 are coupled to each other, sandwiching the rigid internal gear 2 of the harmonic drive gear unit 1 from both sides in a direction parallel to the rotation axis Ax1, that is, in the tooth trace direction D1. Specifically, the input case 111 contacts the rigid internal gear 2 from the input side of the rotation axis Ax1, and the output case 112 contacts the rigid internal gear 2 from the output side of the rotation axis Ax1. In this way, the input case 111, with the rigid internal gear 2 sandwiched between it and the output case 112, is fastened and fixed to the output case 112 by screws (bolts) through a plurality of fixing holes 22. As a result, the input case 111, the output 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 case 111 and the output case 112, constitutes the outer casing of the actuator 100.

[0082] The spline bush 113 is a cylindrical component for connecting the shaft, which serves as the input part 103, to the cam 41. The spline bush 113 is inserted into the cam hole 43 formed in the cam 41, and the shaft, which serves as the input part 103, is inserted through the spline bush 113. Here, the movement of the spline bush 113 is restricted in the rotational direction around the rotation axis Ax1, relative to both the cam 41 and the input part 103, but it is movable at least relative to the input part 103 in the direction parallel to the rotation axis Ax1. This realizes a spline connection structure as the connection structure between the input part 103 and the cam 41. Thus, the cam 41 is movable along the rotation axis Ax1 relative to the input part 103 and rotates together with the input part 103 around the rotation axis Ax1.

[0083] Spacer 114 is a component that fills the gap between the spline bush 113 and the cam 41. First fastener 115 is a component that prevents the spline bush 113 from coming out of the cam 41. First fastener 115 is made of, for example, an E-ring and is attached to the spline bush 113 at the input side of the rotation axis Ax1 as seen from the cam 41. Second fastener 116 is a component that prevents the input portion 103 from coming out of the spline bush 113. Second fastener 116 is made of, for example, an E-ring and is attached to the input portion 103 so as to contact the spline bush 113 from the output side of the rotation axis Ax1.

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

[0085] In this embodiment, lubricant Lb1 is sealed inside the outer casing of the actuator 100, which is composed of an input case 111, an output case 112, and a rigid internal gear 2. In other words, a "lubricant reservoir" capable of storing liquid or gel-like lubricant Lb1 exists within the space surrounded by the input case 111, the output case 112, and the rigid internal gear 2.

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

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

[0088] (3.3) Joint devices for robots Next, the configuration of the robot joint device 130 according to this embodiment will be described in more detail.

[0089] As shown in Figure 4, the robot joint device 130 according to this embodiment comprises the harmonic drive gear device 1 according to this embodiment, a first member 131, and a second member 132. In other words, the robot joint device 130 comprises the rigid internal gear 2, flexible external gear 3, and wave generator 4 that constitute the harmonic drive gear device 1, as well as the first member 131 and the second member 132.

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

[0091] Here, the first member 131 and the second member 132 only need to be directly or indirectly fixed to the rigid internal gear 2 and the flexible external gear 3, respectively. In the example in Figure 4, the first member 131 is indirectly connected (fixed) to the rigid internal gear 2 by being coupled to the output side case 112. Similarly, the second member 132 is indirectly connected (fixed) to the flexible external gear 3 by being coupled to the output section 102.

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

[0093] (4) Detailed configuration of each part Next, the configuration of each part of the harmonic drive gear 1 according to this embodiment will be described in more detail with reference to Figures 1A to 2B, 5 and 6. Figure 5 is a schematic cross-sectional view showing an enlarged view of the main part in the area corresponding to Figure 1B. Figure 6 is a schematic view showing an enlarged view of region Z1 in Figure 5.

[0094] (4.1) Through hole In this embodiment, as shown in Figures 1A and 1B, at least one of the outer ring 421 of the bearing 42 and the external teeth 31 of the flexible external gear 3 is provided with a through hole H1 that penetrates radially and leads to the gap X1 between the outer ring 421 and the flexible external gear 3. In other words, at least one of the inner circumferential surface 425 (see Figure 5) of the outer ring 421 of the bearing 42, which is the rolling surface of the plurality of rolling elements 423, and the outer circumferential surface of the external teeth 31 of the flexible external gear 3, which is the meshing surface with the internal teeth 21, is connected to the gap X1 through the through hole H1. Therefore, lubricant Lb1 can be supplied to the gap X1 between the outer ring 421 and the flexible external gear 3 through the through hole H1.

[0095] In other words, the harmonic drive gear 1 according to this embodiment provides a through hole H1, which allows lubricant Lb1 to be supplied to the contact area between the flexible external gear 3 and the wave generator 4 via the through hole H1, thereby maintaining a sufficient amount of lubricant Lb1 at the contact area. As a result, "lubricant depletion" is prevented, and the surface of the contact area between the outer ring 421 and the flexible external gear 3 is covered with lubricant Lb1, suppressing the occurrence of fretting wear. Therefore, the harmonic drive gear 1 according to this embodiment is less prone to malfunctions caused by fretting wear between the outer ring 421 and the flexible external gear 3, and can provide a harmonic drive gear 1 that is less likely to experience a decrease in reliability.

[0096] By the way, the through hole H1 only needs to be provided in at least one of the outer ring 421 and the external teeth 31 of the flexible external gear 3. In this disclosure, when distinguishing between the through holes H1 provided in the outer ring 421 and the external teeth 31 of the flexible external gear 3, the through hole H1 provided in the outer ring 421 is called the "first through hole," and the through hole H2 (see Figure 12B) provided in the external teeth 31 of the flexible external gear 3 is called the "second through hole." In this embodiment, as an example, the through hole H1 is provided only in the outer ring 421 of the two external teeth 31 of the flexible external gear 3. In other words, in this embodiment, the through hole H1 includes the "first through hole" provided in the outer ring 421. On the other hand, the through hole H2 (second through hole) on the external teeth 31 side of the flexible external gear 3 will be explained in "(8) Modified Examples."

[0097] Furthermore, "penetrating along the radial direction" as used in this disclosure means penetrating along the radial direction, that is, the radial direction perpendicular to the rotation axis Ax1. In other words, if the through hole H1 is provided in the outer ring 421 as in this embodiment, the through hole H1 only needs to penetrate between the inner circumferential surface 425 and the outer circumferential surface 424, which are both radial surfaces of the outer ring 421, and may be inclined with respect to the radial direction, for example.

[0098] First, the shape and dimensions of the through-hole H1 in this embodiment will be described with reference to Figure 5.

[0099] The through-hole H1 (first through-hole) provided in the outer ring 421 penetrates the outer ring 421 radially. As a result, one opening surface of the through-hole H1 faces the gap X1 between the outer ring 421 and the flexible external gear 3, and the other opening surface of the through-hole H1 opens to the inner circumferential surface 425 of the outer ring 421. Therefore, one end of the through-hole H1 connects to the gap X1 between the outer ring 421 and the flexible external gear 3, and the other end connects to the space between the inner circumferential surface 425 of the outer ring 421 and the outer circumferential surface of the inner ring 422. Consequently, the space between the inner circumferential surface 425 of the outer ring 421 and the outer circumferential surface of the inner ring 422, where the multiple rolling elements 423 are arranged, communicates with the gap X1 between the outer ring 421 and the flexible external gear 3 via the through-hole H1.

[0100] Furthermore, the through-hole H1 is a round hole with a circular (perfectly circular) cross-sectional shape perpendicular to the radial direction. In this embodiment, as an example, the center line of the through-hole H1 is parallel to the radial direction. In other words, the through-hole H1 is a hole that extends straight in the radial direction from the inner circumferential surface 425 to the outer circumferential surface 424 of the outer ring 421. Moreover, the cross-sectional shape of the through-hole H1 perpendicular to the radial direction is the same shape along the entire length of the through-hole H1 in the radial direction. In other words, a cylindrical space is formed inside the through-hole H1.

[0101] Here, the diameter φ1 of the through hole H1 (see Figure 5) is the smaller of either 0.1 times or less the diameter φ2 of each of the multiple rolling elements 423 (see Figure 5), or 1.0 mm or less. The diameter φ1 of the through hole H1 referred to here is its diameter if the cross-sectional shape of the through hole H1 is a perfect circle, and if the cross-sectional shape of the through hole H1 is non-circular (e.g., elliptical), it refers to its dimension in the direction of the minor axis. In this embodiment, as an example, the diameter φ1 of the through hole H1 is 0.1 times or less the diameter φ2 of the rolling element 423, and 1.0 mm or less. With such a diameter φ1 of the through hole H1, the lubricant Lb1 can be efficiently supplied through the through hole H1 to the gap X1 between the outer ring 421 and the flexible external gear 3.

[0102] According to the configuration described above, the space between the outer ring 421 and the inner ring 422 is connected to the gap X1 between the outer ring 421 and the flexible external gear 3 via the through hole H1, so that the lubricant Lb1 between the outer ring 421 and the inner ring 422 is supplied to the gap X1 through the through hole H1. In Figure 5, the flow of lubricant Lb1 in the through hole H1 is schematically represented by dashed arrows. In particular, when the bearing 42 operates and the multiple rolling elements 423 rotate, the rolling elements 423 function as a pump, making it possible to send the lubricant Lb1 between the outer ring 421 and the inner ring 422 to the gap X1 via the through hole H1. As a result, "lubricant depletion," where lubricant Lb1 is insufficient or depleted at the contact point between the outer ring 421 and the flexible external gear 3, is prevented, and the occurrence of fretting wear is suppressed.

[0103] In short, the harmonic drive gear 1 according to this embodiment is equipped with a pump structure that supplies lubricant Lb1 to the gap X1 through the through hole H1 when the flexible external gear 3 rotates relative to the rigid internal gear 2. When the flexible external gear 3 rotates relative to the rigid internal gear 2, the multiple rolling elements 423 of the bearing 42 roll in the circumferential direction of the outer ring 421, so as described above, the multiple rolling elements 423 function as a pump. In other words, the multiple rolling elements 423 constitute the pump structure. In particular, in this embodiment, the rolling elements 423 roll in the space between the outer ring 421 and the inner ring 422, which increases the pressure in the space between the outer ring 421 and the inner ring 422, so the lubricant Lb1 between the outer ring 421 and the inner ring 422 is pushed out towards the gap X1 through the through hole H1. In this way, the rolling element 423 constitutes a positive displacement pump, similar to a vane pump, and pushes the lubricant Lb1 towards the gap X1 with sufficient pressure, making it easy to supply a sufficient amount of lubricant Lb1 into the gap X1.

[0104] Furthermore, the opening of the through hole H1 on the inner circumferential surface 425 side of the outer ring 421 opens to the bottom surface of the rolling groove 426 formed on the inner circumferential surface 425 of the outer ring 421. In other words, a rolling groove 426 extending circumferentially around the entire circumference of the outer ring 421 is formed in the center of the inner circumferential surface 425 in the width direction (tooth trace direction D1), and multiple rolling elements 423 roll along the rolling groove 426. A similar rolling groove 427 is formed on the outer circumferential surface of the inner ring 422, and multiple rolling elements 423 are held between these opposing rolling grooves 426 and 427. The through hole H1 is positioned in the range where the rolling groove 426 is formed in the width direction (tooth trace direction D1) of the outer ring 421, so as to open to the bottom surface of the rolling groove 426 of the outer ring 421.

[0105] Furthermore, in this embodiment, the through hole H1 is positioned at the same location as the centers of the multiple rolling elements 423 in a direction parallel to the rotation axis Ax1 (tooth trace direction D1). In other words, the through hole H1 is positioned at the center of the rolling groove 426 in the width direction (tooth trace direction D1) of the outer ring 421. With this configuration, the centers of the multiple rolling elements 423 pass over the opening surface of the through hole H1, and when the rolling elements 423 rotate, the rolling elements 423 act efficiently as pumps, making it easier to send lubricant Lb1 into the gap X1 via the through hole H1. In addition, it is known that the outer ring 421 and the flexible external gear 3 mainly come into contact at both ends of the outer ring 421 in the width direction (tooth trace direction D1). Therefore, because the through-hole H1 is formed in the center of the width direction (tooth trace direction D1) of the outer ring 421, a reduction in the strength of the outer ring 421 due to the through-hole H1 is less likely to occur when the outer ring 421 comes into contact with the flexible external gear 3.

[0106] Here, as shown in Figure 5, the rolling grooves 426 and 427 have a cross-sectional shape that is perpendicular to the circumferential direction of the outer ring 421 and is formed in an arc shape. The curvature of the arc in the cross-sectional shape of the rolling grooves 426 and 427 is greater than the curvature of each of the multiple rolling elements 423. In other words, the radius of curvature of the arc in the cross-sectional shape of the rolling grooves 426 and 427 is smaller than the radius of curvature of the rolling elements 423. Therefore, when multiple rolling elements 423 are held in place between the rolling grooves 426 and 427, a certain amount of gap is secured between the bottom surface of the rolling grooves 426 and 427 and the surface of each rolling element 423. In other words, as shown in Figure 5, each rolling element 423 is supported at four points: at both ends of the rolling groove 426 in the width direction (tooth trace direction D1) on the outer ring 421, and at both ends of the rolling groove 427 in the width direction (tooth trace direction D1) on the inner ring 422. However, in reality, a load is applied between the outer ring 421 and the inner ring 422 in the relative thrust direction (direction parallel to the rotation axis Ax1), so the rolling elements 423 are supported at a pair of ends that are diagonally opposite each other.

[0107] Therefore, the opening surface of the through hole H1 formed on the bottom surface of the rolling groove 426 faces the surface of the rolling element 423 through the gap described above. In short, in this embodiment, in the radial direction, a distance of a predetermined value or more is secured between the raceways of the multiple rolling elements 423 and the opening surface of the (first) through hole H1 provided in the outer ring 421 on the inner circumferential surface 425 side of the outer ring 421. In other words, even when the rolling element 423 is in a position corresponding to the through hole H1, a distance (gap) of a predetermined value or more is secured between the opening surface of the through hole H1 and the rolling element 423, and the through hole H1 is not blocked by the rolling element 423. As a result, when the multiple rolling elements 423 roll, even if they pass over the through hole H1, the rolling elements 423 do not collide with the opening edge of the through hole H1. As a result, when the rolling element 423 passes over the through hole H1, the impact caused by the rolling element 423 colliding with the opening edge of the through hole H1 can be avoided, making it easier to protect the outer ring 421 and the rolling element 423 from impact.

[0108] (4.2) Number and arrangement of through holes Next, the number and arrangement of the through holes H1 in this embodiment will be described with reference to Figures 2A and 2B.

[0109] As shown in Figure 2A, the through-hole H1 includes a plurality of first through-holes provided in the outer ring 421 so as to be aligned in the circumferential direction of the outer ring 421. In this embodiment, since the through-hole H1 consists only of the first through-holes provided in the outer ring 421, all of the plurality of through-holes H1 are arranged in the circumferential direction of the outer ring 421. In this embodiment, as an example, the outer ring 421 is provided with three through-holes H1. Therefore, lubricant Lb1 can be supplied to the gap X1 between the outer ring 421 and the flexible external gear 3 through the through-holes H1 at multiple locations (three locations in this embodiment) in the circumferential direction of the outer ring 421. As a result, compared to the case where only one through-hole H1 is provided in the circumferential direction of the outer ring 421, lubricant Lb1 is more easily supplied over the entire circumferential area of ​​the outer ring 421 in the gap X1.

[0110] Here, as shown in Figure 2A, the spacing P1 between the multiple through holes H1 (first through holes) is a value other than a multiple of the spacing P2 between the multiple rolling elements 423. In this embodiment, as an example, the bearing 42 has 26 rolling elements 423 and the outer ring 421 has 3 through holes H1. The 26 rolling elements 423 and the 3 through holes H1 are each provided at equal pitches (equal spacing) in the circumferential direction of the outer ring 421. Therefore, the spacing P1 between the 3 through holes H1 in the circumferential direction of the outer ring 421 is 120 degrees (=360 degrees ÷ 3), and the spacing P2 between the 26 rolling elements 423 in the circumferential direction of the outer ring 421 is 13.85 degrees (=360 degrees ÷ 26). Here, the interval P1 is the value expressed as the angle around the rotation axis Ax1, representing the distance between the centers of two circumferentially adjacent through holes H1 of the outer ring 421, and similarly, the interval P2 is the value expressed as the angle around the rotation axis Ax1, representing the distance between the centers of two circumferentially adjacent rolling elements 423 of the outer ring 421. In this embodiment, the interval P1 is set to a value that is not divisible by the interval P2, such that multiplying the interval P2 (13.85 degrees) of the multiple rolling elements 423 by any integer will not result in a value that matches the interval P1 (120 degrees) of the multiple through holes H1.

[0111] This prevents the simultaneous presence of rolling elements 423 at positions corresponding to all through-holes H1. In other words, when one rolling element 423 is located at a position corresponding to one through-hole H1, no rolling elements 423 will be located at the positions corresponding to the other two through-holes H1. Therefore, in the harmonic drive gear 1 according to this embodiment, it is possible to avoid the generation of relatively large impacts that may occur when multiple rolling elements 423 are simultaneously fitted into (or disengaged from) multiple through-holes H1, and the outer ring 421 and rolling elements 423 are more easily protected from impact. In addition, the pumping action due to the rolling of the rolling elements 423 becomes more efficient compared to the case where rolling elements 423 are located on all through-holes H1 simultaneously.

[0112] (4.3) Inner surface shape of flexible external gear Next, the surface condition of the inner circumferential surface 301 of the flexible external gear 3 in this embodiment will be described with reference to Figures 5 and 6.

[0113] In this embodiment, as described above, the portion of the bearing 42 facing the outer ring 421 on the inner circumferential surface 301 of the flexible external gear 3 includes a small-diameter portion 305 that is narrower than the outer ring 421 in the tooth trace direction D1 of the external teeth 31, and a large-diameter portion 306 that is larger in diameter than the small-diameter portion 305. Because the large-diameter portion 306 is relatively larger in diameter than the small-diameter portion 305, it is a portion where contact with the outer ring 421 is less likely to occur in the width direction (tooth trace direction D1) of the outer ring 421. In other words, the diameter of the portion of the inner circumferential surface 301 of the flexible external gear 3 facing the outer ring 421 is not constant, and includes a small-diameter portion 305 that is relatively smaller in diameter and a large-diameter portion 306 that is relatively larger in diameter. Therefore, with the wave generator 4 fitted inside the body 321 of the flexible external gear 3, only the smaller diameter portion 305 of the two larger diameter portions 306 will be in contact with the outer circumferential surface 424 of the outer ring 421.

[0114] In other words, when the bearing 42 is not elastically deformed (when the cam 41 is not assembled to the bearing 42), the outer diameter of the outer ring 421 is the same as the diameter φ11 of the small diameter portion 305 of the flexible external gear 3 when no elastic deformation has occurred. On the other hand, the diameter φ12 of the large diameter portion 306 (see Figure 6) is larger than the diameter φ11 of the small diameter portion 305. Therefore, when the wave generator 4 is fitted inside the body portion 321 of the flexible external gear 3, the large diameter portion 306 and the outer circumferential surface 424 of the outer ring 421 are not in contact.

[0115] Furthermore, the small-diameter portion 305 of the inner circumferential surface 301 of the flexible external gear 3, which is the contact area with the outer ring 421, is narrower than the outer ring 421 in the tooth trace direction D1 of the external teeth 31 (the direction parallel to the rotation axis Ax1). Therefore, on the inner circumferential surface 301 of the flexible external gear 3, it is less likely that a "step" will occur due to localized wear (greater than other areas) at the parts where the ends of the outer ring 421 in the width direction make contact.

[0116] Here, there is a difference of 5 μm to 30 μm between the radius of the small diameter portion 305 and the radius of the large diameter portion 306. That is, as shown in Figure 6, when comparing half of the diameter φ11 of the small diameter portion 305 with half of the diameter φ12 of the large diameter portion 306, the difference is between 5 μm and 30 μm. As a result, a stepped intermediate portion 307 with a height difference of 5 μm to 30 μm is created between the small diameter portion 305 and the large diameter portion 306. In this way, by providing a sufficient height difference between the small diameter portion 305 and the large diameter portion 306, a sufficient gap X1 is secured between the large diameter portion 306 and the outer ring 421, and contact between the large diameter portion 306 and the outer ring 421 is suppressed.

[0117] Furthermore, in this embodiment, the dimension L1 (width) of the small diameter portion 305 of the external teeth 31 in the tooth trace direction D1 is 1 / 2 or more of the diameter (diameter φ2) of the rolling element 423 of the bearing 42. That is, the dimension L1 of the small diameter portion 305 of the external teeth 31 in the tooth trace direction D1 is set to be smaller than the dimension of the outer ring 421 in the tooth trace direction D1 and to be 1 / 2 or more of the diameter φ2 of the rolling element 423. For example, the dimension L1 of the small diameter portion 305 may be larger than the diameter φ2 of the rolling element 423 as shown in Figure 5, or it may be less than or equal to the diameter φ2 of the rolling element 423, and is not limited to this example.

[0118] Here, as shown in Figure 5, in this embodiment, large-diameter portions 306 are provided on both sides of the small-diameter portion 305 in the tooth trace direction D1 of the external teeth 31. That is, the large-diameter portion 306 includes a first large-diameter portion 306A and a second large-diameter portion 306B located on both sides of the small-diameter portion 305 in the tooth trace direction D1 of the external teeth 31. The first large-diameter portion 306A is located on the output side of the rotation axis Ax1 when viewed from the small-diameter portion 305, and the second large-diameter portion 306B is located on the input side of the rotation axis Ax1 when viewed from the small-diameter portion 305. In this embodiment, the same diameter φ12 is used for both the first large-diameter portion 306A and the second large-diameter portion 306B. As a result, on the inner circumferential surface 301 of the flexible external gear 3, the "steps" caused by localized wear (larger than other parts) at the parts where both ends in the width direction of the outer ring 421 make contact are less likely to occur.

[0119] In this embodiment, all parts of the inner circumferential surface 301 of the flexible external gear 3, except for the small diameter portion 305, have the same diameter as the large diameter portion 306 (φ12). In other words, all parts of the body portion 321 of the flexible external gear 3, except for the small diameter portion 305, have an inner diameter of φ12, the same as the large diameter portion 306. As a result, the "steps" caused by localized wear (greater than other parts) at the points where the outer ring 421 contacts the inner circumferential surface 301 of the flexible external gear 3 are less likely to occur.

[0120] Furthermore, as described above, the flexible external gear 3 is cylindrical with an opening surface 35 on one side in the tooth trace direction D1 of the external teeth 31. Here, the large diameter portion 306 is located at least on the opening surface 35 side relative to the small diameter portion 305. In short, the large diameter portion 306 is formed at least on the opening surface 35 side (input side of the rotation axis Ax1) of the body portion 321 of the flexible external gear 3, as viewed from the small diameter portion 305. In this embodiment, as described above, large diameter portions 306 are provided on both sides of the small diameter portion 305, and of the first large diameter portion 306A and the second large diameter portion 306B, the second large diameter portion 306B is located on the opening surface 35 side relative to the small diameter portion 305. This makes it possible to suppress contact between the inner circumferential surface of the flexible external gear 3 and the outer ring 421 on the opening surface 35 side, where the contact with the outer ring 421 becomes particularly strong due to the elastic deformation of the flexible external gear 3.

[0121] Furthermore, in this embodiment, the small-diameter portion 305 is integrated with the flexible external gear 3. In other words, the small-diameter portion 305 is formed seamlessly and continuously with the body portion 321 of the flexible external gear 3. This improves the positional accuracy of the small-diameter portion 305 and makes it possible to easily form both the small-diameter portion 305 and the large-diameter portion 306.

[0122] Furthermore, the flexible external gear 3 is made of a softer material than at least the outer ring 421 of the bearing 42. In other words, in this embodiment, the outer ring 421 is harder than the inner circumferential surface 301 of the flexible external gear 3. In this embodiment in particular, the outer ring 421 is made of a material that is hard and tough, while the flexible external gear 3 is made of a material that is less hard than the outer ring 421. Therefore, when the flexible external gear 3 and the outer ring 421 come into contact, the inner circumferential surface 301 of the flexible external gear 3, which is relatively less hard, wears preferentially over the outer ring 421. As a result, wear on the outer ring 421 is suppressed.

[0123] In other words, when the wave drive gear 1 is in operation, the flexible external gear 3 and the outer ring 421 come into contact, and the flexible external gear 3, which has a relatively lower surface hardness, wears more aggressively than the outer ring 421. When two parts with different surface hardnesses (flexible external gear 3 and outer ring 421) come into contact, the wear of the relatively softer flexible external gear 3 progresses, thereby suppressing the wear of the relatively harder outer ring 421. Therefore, even if the intermediate portion 307 that occurs between the small diameter portion 305 and the large diameter portion 306 comes into contact with the outer ring 421, the outer ring 421 is unlikely to develop a "step" due to localized wear (greater than other parts) at the point where the intermediate portion 307 makes contact.

[0124] (4.4) Surface hardness Next, the surface hardness of the inner circumferential surface 301 of the flexible external gear 3 and the outer ring 421 of the bearing 42 in this embodiment will be described.

[0125] In this embodiment, as described above, the outer ring 421 has higher hardness than the inner circumferential surface 301 of the flexible external gear 3. In other words, the surface of the outer ring 421 is harder than the inner circumferential surface 301 of the flexible external gear 3. In this disclosure, "hardness" refers to the degree of hardness of an object. The hardness of a metal is expressed, for example, by the size of the indentation made when a steel ball is pressed with a certain pressure. Specifically, examples of metal hardness include Rockwell hardness (HRC), Brinell hardness (HB), Vickers hardness (HV), or Shore hardness (Hs). In this embodiment, unless otherwise specified, hardness is expressed in terms of Vickers hardness (HV). Means for increasing (hardening) the hardness of a metal part include, for example, alloying or heat treatment.

[0126] Specifically, the surface hardness of the inner circumferential surface 301 of the flexible external gear 3, which is relatively lower in hardness compared to the outer ring 421, is preferably HV (Vickers hardness) 450 or less. In this embodiment, as an example, the surface hardness of the inner circumferential surface 301 of the flexible external gear 3 is selected within the range of HV400 or more and HV450 or less. The lower limit of the surface hardness of the inner circumferential surface 301 of the flexible external gear 3 is not limited to HV400, but may be, for example, HV280, HV290, HV300, HV310, HV320, HV330, HV340, HV350, HV360, HV370, HV380 or HV390, etc. Similarly, the upper limit of the surface hardness of the inner circumferential surface 301 of the flexible external gear 3 is not limited to HV450, but may be, for example, HV460, HV470, HV480, HV490, HV500, HV510, HV520, HV530, HV540, or HV550.

[0127] In contrast, the surface hardness of the outer ring 421 (and its outer surface 424), which is relatively harder than the inner surface 301 of the flexible external gear 3, is preferably HV700 or higher. In this embodiment, as an example, the surface hardness of the outer ring 421 is selected within the range of HV700 or higher and HV770 or lower. The lower limit of the surface hardness of the outer ring 421 is not limited to HV700, but may be, for example, HV600, HV610, HV620, HV630, HV640, HV650, HV660, HV670, HV680 or HV690, etc. Similarly, the upper limit of the surface hardness of the outer ring 421 is not limited to HV770, but may be, for example, HV780, HV790, HV800, HV810, HV820, HV830, HV840, HV850, HV860, or HV870.

[0128] By setting the surface hardness as described above, the hardness difference (difference in hardness) between the inner surface 301 of the flexible external gear 3 and the outer ring 421 becomes HV250 or higher and HV370 or lower. In other words, the surface hardness of the outer ring 421 is set to be HV250 or higher compared to the surface hardness of the inner surface 301 of the flexible external gear 3. In this way, there is a sufficient hardness difference between the inner surface 301 of the flexible external gear 3 and the outer ring 421, so when the flexible external gear 3 and the outer ring 421 come into contact, the inner surface 301 of the flexible external gear 3, which has relatively lower hardness, will wear down, while the wear of the outer ring 421 will be suppressed.

[0129] It is not mandatory for the surface hardness of the flexible external gear 3 and the outer ring 421 to be defined by Vickers hardness (HV). The surface hardness of the internal teeth 21 and external teeth 31 may be defined by other hardness measures, such as Rockwell hardness (HRC), Brinell hardness (HB), or Shore hardness (Hs). For example, when the surface hardness is defined by Rockwell hardness, the surface hardness of the outer ring 421 is preferably selected within the range of HRC60 or higher and HRC63 or lower.

[0130] Furthermore, such hardness differences are established not only between the flexible external gear 3 and the outer ring 421, but also, for example, between the internal teeth 21 and the external teeth 31.

[0131] (4.5) Tooth line modification Next, the tooth contour modification of the internal teeth 21 and external teeth 31 in this embodiment will be described.

[0132] As a premise, the internal tooth 21 has a tooth root 212 and a tooth tip 213, as shown in Figure 1B. Since the internal tooth 21 is provided on the inner circumferential surface of the rigid internal gear 2, the tooth root 212 of the internal tooth 21 corresponds to the inner circumferential surface of the rigid internal gear 2, and the tooth tip 213 protrudes inward from the inner circumferential surface of the rigid internal gear 2 (towards the center of the rigid internal gear 2).

[0133] On the other hand, as shown in Figure 1B, the external teeth 31 have a tooth root 312 and a tooth tip 313. Since the external teeth 31 are provided on the outer circumferential surface of the flexible external gear 3 (body 321), the tooth root 312 of the external teeth 31 corresponds to the outer circumferential surface of the flexible external gear 3 (body 321), and the tooth tip 313 protrudes outward from the outer circumferential surface of the flexible external gear 3 (body 321).

[0134] At the meshing position between the internal teeth 21 and the external teeth 31, the tooth tips 313 of the external teeth 31 are inserted between a pair of adjacent tooth tips 213 of the internal teeth 21, thus meshing the internal teeth 21 and the external teeth 31. At this time, the tooth tips 313 of the external teeth 31 face the tooth roots 212 of the internal teeth 21, and the tooth tips 213 of the internal teeth 21 face the tooth roots 312 of the external teeth 31. Ideally, a small gap is maintained between the tooth roots 212 of the internal teeth 21 and the tooth tips 313 of the external teeth 31, and between the tooth roots 312 of the external teeth 31 and the tooth tips 213 of the internal teeth 21. In this state, the tooth surfaces of the internal teeth 21 and the external teeth 31 that face each other in the tooth thickness direction come into contact, and power is transmitted between the rigid internal gear 2 and the flexible external gear 3.

[0135] Furthermore, the internal tooth 21 has chamfered portions 211 at both ends in the tooth trace direction D1. The chamfered portions 211 are C-surfaces that reduce the amount of protrusion of the internal tooth 21 toward both sides in the tooth trace direction D1, and are basically parts that do not contribute to the meshing between the internal tooth 21 and the external tooth 31. In other words, the chamfered portions 211 of the internal tooth 21 do not contact the external tooth 31 even at the meshing position between the internal tooth 21 and the external tooth 31. Similarly, the external tooth 31 has chamfered portions 311 at both ends in the tooth trace direction D1. The chamfered portions 311 are C-surfaces that reduce the amount of protrusion of the internal tooth 21 toward both sides in the tooth trace direction D1, and are basically parts that do not contribute to the meshing between the internal tooth 21 and the external tooth 31. In other words, the chamfered portions 311 of the external tooth 31 do not contact the internal tooth 21 even at the meshing position between the internal tooth 21 and the external tooth 31.

[0136] In this embodiment, the internal teeth 21 of the rigid internal gear 2 have tooth trace modification portions 210. That is, the harmonic drive gear 1 has tooth trace modification applied to at least the internal teeth 21. The tooth trace modification portions 210 of the internal teeth 21 are provided at at least one end in the tooth trace direction D1. In other words, the internal teeth 21 have tooth trace modification portions 210 at at least one end in the tooth trace direction D1. 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.

[0137] Furthermore, in this embodiment, the external teeth 31 of the flexible external gear 3 also have tooth trace modification portions 310. In other words, the harmonic drive gear 1 has tooth trace modification applied not only to the internal teeth 21 but also to the external teeth 31. The tooth trace modification portions 210 of the external teeth are provided at at least one end in the tooth trace direction D1. In other words, the external teeth 31 have tooth trace modification portions 310 at at least one end in the tooth trace direction D1 of the external teeth 31. In this embodiment, the tooth trace modification portions 310 are provided at both ends of the external teeth 31 in the tooth trace direction D1.

[0138] Thus, in the harmonic drive gear 1 according to this embodiment, at least one of the internal teeth 21 and the external teeth 31 has tooth guide modification parts 210, 310. The tooth guide modification parts 210, 310 make it less likely for stress concentration to occur due to excessive tooth contact between the internal teeth 21 and the external teeth 31, and as a result, the tooth contact between the internal teeth 21 and the external teeth 31 can be improved. Therefore, foreign matter such as chipping or wear caused by contact between the internal teeth 21 and the external teeth 31 is less likely to occur, and a harmonic drive gear 1 that is less prone to a decrease in reliability can be realized.

[0139] (5) Effect Next, the operation of the harmonic drive gear 1 according to this embodiment will be described in more detail.

[0140] In a harmonic drive gear 1 that does not have a small diameter section 305 and a large diameter section 306, especially with long-term use, wear may occur on the contact area between the outer ring 421 of the bearing 42 of the wave generator 4 on the inner circumferential surface 301 of the flexible external gear 3 and the wave generator 4, due to the rotation of the wave generator 4 fitted inside the flexible external gear 3. This wear may cause steps to form on the inner circumferential surface 301 of the flexible external gear 3 at both ends (corners) of the outer ring 421 in the width direction (direction of the rotation axis Ax1). When such steps are present, the outer ring 421 repeatedly collides with these steps as the flexible external gear 3 deforms (bends), which may lead to damage to the flexible external gear 3 or the wave generator 4 (bearing 42), potentially affecting the reliability of the harmonic drive gear 1.

[0141] The reason for these steps is that the flexible external gear 3 undergoes frequent elastic deformation. In other words, while the cam 41 of the wave generator 4 rotates once, the flexible external gear 3 undergoes elastic deformation twice, with one direction (for example, the up and down direction in Figure 2A) becoming the major axis of an ellipse. Therefore, as the cam 41 rotates at high speed, the flexible external gear 3 undergoes repeated elastic deformation at high speed, and with each repetition of this elastic deformation, the "contact" between the wave generator 4 and the inner circumferential surface 301 of the flexible external gear 3 becomes stronger.

[0142] More specifically, when the flexible external gear 3 is undergoing elastic deformation, the end on the side of the opening surface 35 in the direction of the rotation axis Ax1 deforms more significantly than the end on the side of the bottom surface 322, resulting in a shape closer to an ellipse. Therefore, when the flexible external gear 3 is undergoing elastic deformation, the inner circumferential surface 301 of the body 321 of the flexible external gear 3 includes a tapered surface 302 that is inclined at an angle θ1 with respect to the rotation axis Ax1, as shown in Figure 7. The inclination angle θ1 of the tapered surface 302 is defined as positive (positive) when the inclination direction toward the opening surface 35 and negative (negative) when the inclination direction toward the opposite side of the opening surface 35, and changes in accordance with the elastic deformation of the flexible external gear 3. In other words, when the flexible external gear 3 is viewed from the opening surface 35 side, the inclination angle θ1 of the tapered surface 302 is maximum in the positive direction at both ends along the major axis of the ellipse (the "major axis side" in Figure 7), and the inclination angle θ1 of the tapered surface 302 is maximum in the negative direction at both ends along the minor axis of the ellipse (the "minor axis side" in Figure 7). Therefore, on the major axis side of the ellipse, strong "contact" occurs with the inner circumferential surface 301 of the flexible external gear 3 at the corner of the outer ring 421 on the opening surface 35 side, and on the minor axis side of the ellipse, strong "contact" can occur with the inner circumferential surface 301 of the flexible external gear 3 at the corner of the outer ring 421 opposite to the opening surface 35.

[0143] In contrast, in the harmonic drive gear 1 according to this embodiment, the inner circumferential surface 301 of the flexible external gear 3 is provided with a small diameter portion 305 and a large diameter portion 306, and the small diameter portion 305, which is the contact portion with the outer ring 421, is narrower than the outer ring 421 in the tooth trace direction D1 of the external teeth 31. Therefore, as shown in Figure 7, even if the flexible external gear 3 undergoes repeated elastic deformation at high speed, the large diameter portion 306 of the small diameter portion 305 and the large diameter portion 306 will not be in contact with the outer circumferential surface 424 of the outer ring 421. Consequently, on the inner circumferential surface 301 of the flexible external gear 3, it is less likely that "steps" will occur due to localized wear (larger than other parts) at the parts where both ends in the width direction of the outer ring 421 make contact.

[0144] Therefore, in the harmonic drive gear 1 according to this embodiment, the occurrence of "steps" due to localized wear of the inner circumferential surface 301 of the flexible external gear 3 is suppressed, making it less likely for problems caused by such steps to occur, and thus providing a harmonic drive gear 1 that is less prone to a decrease in reliability. Furthermore, since the harmonic drive gear 1 according to this embodiment is less prone to a decrease in reliability, especially during long-term use, it leads to improved transmission efficiency, longer lifespan, and higher performance of the harmonic drive gear 1.

[0145] Furthermore, the harmonic drive gear 1 according to this embodiment also has the effect of reducing the bending moment and bending stress acting on the outer ring 421 of the bearing 42. That is, the bending moment and bending stress acting on the outer ring 421 are determined by the distance in the tooth trace direction D1 between the contact position with the outer ring 421 on the elliptical major axis side and the contact position with the outer ring 421 on the elliptical minor axis side of the inner circumferential surface 301 of the flexible external gear 3. In this embodiment, the small diameter portion 305, which is the contact portion with the outer ring 421, is narrower than the outer ring 421 in the tooth trace direction D1 of the external teeth 31, so this distance is also shortened to be narrower than the outer ring 421. The shorter this distance, the smaller the bending moment and bending stress acting on the outer ring 421 of the bearing 42, so in this embodiment, the bending moment and bending stress acting on the outer ring 421 of the bearing 42 can be reduced.

[0146] Furthermore, when the wave drive gear unit 1 is driven, the point of application of the load acting from the bearing 42 of the wave generator 4 to the flexible external gear 3 on the inner circumferential surface 301 of the flexible external gear 3 is located on the small diameter portion 305, which is the contact point with the outer ring 421. Since the small diameter portion 305 is narrower than the outer ring 421 in the tooth trace direction D1 (parallel to the rotation axis Ax1) of the external teeth 31, the point of application is located on a straight line (in the radial direction) connecting the rolling groove 427 of the inner ring 422 of the bearing 42, the rolling element 423, and the rolling groove 426 of the outer ring 421. Therefore, it becomes less likely for excessive forces other than those in the radial direction to act on the bearing 42 of the wave generator 4, leading to a longer lifespan for the bearing 42.

[0147] Furthermore, in the harmonic drive gear 1 according to this embodiment, the provision of a small-diameter portion 305 and a large-diameter portion 306 on the inner circumferential surface 301 of the flexible external gear 3 makes it possible to suppress damage to the flexible external gear 3 and the wave generator 4 caused by "galling". Specifically, when assembling the flexible external gear 3 and the wave generator 4, or in the initial stages of use of the harmonic drive gear 1, localized adhesive wear called "galling" may occur at the contact points between the flexible external gear 3 and the wave generator 4. According to the harmonic drive gear 1 according to this embodiment, when assembling the flexible external gear 3 and the wave generator 4, the large-diameter portion 306 (especially the second large-diameter portion 306B) of the inner circumferential surface 301 of the flexible external gear 3 functions as a guide for fitting the wave generator 4 into the small-diameter portion 305, thereby suppressing the occurrence of "galling". As a result, the growth of minute wear caused by "galling" can be suppressed, and damage to the flexible external gear 3 and wave generator 4 can be reduced.

[0148] (6) Examples of application Next, examples of applications of the harmonic drive gear 1, actuator 100, and robot joint device 130 according to this embodiment will be described with reference to Figure 8.

[0149] Figure 8 is a cross-sectional view showing an example of a robot 9 using the harmonic drive gear 1 according to this embodiment. This robot 9 is a horizontal articulated robot, a so-called SCARA (Selective Compliance Assembly Robot Arm) type robot.

[0150] As shown in Figure 8, the robot 9 comprises two robotic joint devices 130 (including a harmonic drive gear 1) and a link 91. The two robotic joint devices 130 are provided at two joint locations on the robot 9. The link 91 connects the two robotic joint devices 130. In the example in Figure 8, the harmonic drive gear 1 is a top hat type, not a cup type. That is, the harmonic drive gear 1 illustrated in Figure 8 uses a flexible external gear 3 formed in the shape of a top hat.

[0151] (7) Manufacturing method When manufacturing the harmonic drive gear 1 according to this embodiment, it is preferable to take measures to avoid a reduction in strength due to the provision of the through hole H1, especially when manufacturing the outer ring 421.

[0152] As an example, it is preferable to perform a surface treatment process on the outer ring 421 (particularly the inner circumferential surface 425, which becomes the rolling surface) after the drilling process to form the through hole H1. In other words, it is preferable to leave compressive residual stress around the through hole H1 in the outer ring 421 so that the through hole H1 does not become the starting point for cracking in the outer ring 421. For this purpose, it is preferable to form the through hole H1 before performing a surface treatment process such as quenching on the outer ring 421 and leave compressive residual stress by heat treatment. Alternatively, after heat treatment, the fatigue strength of the outer ring 421 may be improved by applying a shot peening process or the like to modify and harden the surface around the through hole H1 in the outer ring 421 by projecting small spherical projectiles.

[0153] Furthermore, it is even more preferable to create an uneven surface on the outer circumferential surface 424 of the outer ring 421 by shot peening or barrel polishing, etc., after polishing, in order to remove grinding marks (grinding marks). This further suppresses the occurrence of "galling" at the contact area between the flexible external gear 3 and the wave generator 4, especially during the initial use of the wave drive gear unit 1.

[0154] (8) Variations Embodiment 1 is merely one of many embodiments of this disclosure. Embodiment 1 can be modified in various ways depending on the design, etc., as long as the objectives of this disclosure are achieved. Furthermore, the drawings referenced in this disclosure are all schematic diagrams, and the ratios of the size and thickness of each component in the drawings do not necessarily reflect the actual dimensional ratios. The following lists some modifications of Embodiment 1. The modifications described below can be combined and applied as appropriate.

[0155] The through-hole H1 may be located offset from the centers of the multiple rolling elements 423 in a direction parallel to the rotation axis Ax1 (tooth trace direction D1). For example, the through-hole H1 may be located offset from the center of the rolling element 423 toward the opening surface 35, that is, between the center of the rolling element 423 and the opening surface 35 in the tooth trace direction D1. With this configuration, even if a large radial load is applied to the member in which the through-hole H1 is formed (in this case, the outer ring 421) from the rolling elements 423, the load is less likely to act around the through-hole H1, which has the advantage of making it less likely for cracks to start from the through-hole H1.

[0156] Furthermore, the through-hole H1 may be provided at multiple locations in a direction parallel to the rotation axis Ax1 (tooth trace direction D1). Also, in the radial direction, the opening area of ​​the through-hole H1 on the gap X1 side may be smaller than the opening area on the opposite side of the gap X1. That is, in the (first) through-hole H1 provided in the outer ring 421, the opening area of ​​the through-hole H1 on the outer circumferential surface 424 side, which is the gap X1 side, is smaller than the opening area of ​​the through-hole H1 on the inner circumferential surface 425 side, which is the opposite side of the gap X1. This makes it possible to increase the pressure of the lubricant Lb1 supplied to the gap X1 through the through-hole H1.

[0157] Furthermore, through holes H1 and H2 may be provided in both the outer ring 421 and the external teeth 31 of the flexible external gear 3. In this case, the lubricant Lb1 in the space between the outer ring 421 and the inner ring 422 of the bearing 42 can be supplied through the through hole H1 to the gap X1 between the outer ring 421 and the flexible external gear 3. In addition, the lubricant Lb1 in the space between the external teeth 31 and the internal teeth 21 can be supplied through the through hole H2 to the gap X1 between the outer ring 421 and the flexible external gear 3. Therefore, the lubricant Lb1 can be supplied to the gap X1 from both sides (inside and outside) in the radial direction. Here, it is preferable that the (first) through hole H1 and the (second) through hole H2 are located at different positions in the tooth trace direction D1 of the internal teeth 21.

[0158] Furthermore, tooth profile modification of the internal teeth 21 and external teeth 31 is not an essential component of the harmonic drive gear 1. For example, tooth profile modification may not be performed on at least one of the internal teeth 21 and external teeth 31.

[0159] Furthermore, it is not essential for the harmonic drive gear 1 to ensure a distance of a predetermined value or greater between the raceways of the multiple rolling elements 423 and the opening surface of the (first) through hole H1 provided in the outer ring 421 in the radial direction. In other words, even if the rolling elements 423 are located in positions corresponding to the through hole H1, there may be no gap between the opening surface of the through hole H1 and the rolling elements 423, and the through hole H1 may be closed by the rolling elements 423.

[0160] Furthermore, the fact that each rolling element 423 is supported at four points in the bearing 42 is not an essential configuration for the harmonic drive gear 1; for example, each rolling element 423 may be supported at two points.

[0161] Furthermore, the harmonic drive gear 1 is not limited to the cup type described in Embodiment 1, but may also be of other types, such as a top hat type, ring type, differential type, flat type (pancake type), or shield type. For example, even a top hat type harmonic drive gear 1 has a cylindrical flexible external gear 3 having an opening surface 35 on one side in the tooth trace direction D1, similar to the cup type. That is, the top hat type flexible external gear 3 has a flange portion at one end of the rotating shaft Ax1 and an opening surface 35 at the end opposite to the flange portion. Even a top hat type flexible external gear 3 has external teeth 31 at the end on the opening surface 35 side, and a wave generator 4 is fitted into it.

[0162] Furthermore, the configuration of the actuator 100 is not limited to the configuration described in Embodiment 1, and can be modified as appropriate. For example, the connection structure between the input section 103 and the cam 41 is not limited to a spline connection structure; an Oldham joint or the like may be used. By using an Oldham joint as the connection structure between the input section 103 and the cam 41, the misalignment between the input-side rotation axis Ax1 and the wave generator 4 (cam 41) can be canceled out, and furthermore, the misalignment between the rigid internal gear 2 and the flexible external gear 3 can be canceled out. Moreover, the cam 41 does not need to be movable along the rotation axis Ax1 relative to the input section 103.

[0163] Furthermore, the application examples of the harmonic drive gear unit 1, actuator 100, and robot joint unit 130 according to this embodiment are not limited to horizontal articulated robots as described above, but may also include, for example, industrial robots other than horizontal articulated robots, or robots other than industrial robots. Examples of industrial robots other than horizontal articulated robots include vertical articulated robots or parallel link robots. Examples of robots other than industrial robots include household robots, nursing care robots, or medical robots.

[0164] Furthermore, the bearing 42 is not limited to a deep groove ball bearing, but may also be an angular contact ball bearing, for example. Moreover, the bearing 42 is not limited to a ball bearing, but may also be a roller bearing such as a cylindrical roller bearing, needle roller bearing, or tapered roller bearing, in which the rolling elements 423 are not ball-shaped "rollers". Even if the rolling elements 423 are not ball-shaped (spherical), the rolling of the rolling elements 423 generates a pressure difference, and the rolling elements 423 function as a pump structure.

[0165] Furthermore, the material of each component of the wave drive gear unit 1, actuator 100, or robot joint unit 130 is not limited to metal, but may be, for example, a resin such as engineering plastic.

[0166] Furthermore, the lubricant Lb1 is not limited to liquid substances such as lubricating oil, but may also be a gel-like substance such as grease.

[0167] Furthermore, the number and arrangement of the through holes H1 are not limited to those described in Embodiment 1. For example, there may be one, two, or four or more through holes H1. Moreover, when multiple through holes H1 are provided, the spacing P1 between the multiple through holes H1 may be a multiple of the spacing P2 between the multiple rolling elements 423, and it is not essential that the multiple through holes H1 are arranged at equal pitches.

[0168] Furthermore, the small-diameter portion 305 may be constructed separately from the flexible external gear 3. For example, by attaching a strip-shaped member to a part of the tooth trace direction D1 of the external teeth 31 on the inner circumferential surface 301 of the flexible external gear 3 over its entire circumference, the inner circumferential surface of the member can be made into the small-diameter portion 305. Also, the outer ring 421 may have a hardness of similar magnitude to the inner circumferential surface 301 of the flexible external gear 3, or it may have a lower hardness than the inner circumferential surface 301 of the flexible external gear 3.

[0169] Furthermore, it is not essential that the large-diameter portion 306 be provided on both sides of the small-diameter portion 305 in the tooth trace direction D1 of the external tooth 31. That is, the large-diameter portion 306 may be provided only on one side of the small-diameter portion 305 (either on the side of the opening surface 35 or on the opposite side of the opening surface 35) in the tooth trace direction D1. Moreover, it is not essential that the large-diameter portion 306 be located at least on the side of the opening surface 35 relative to the small-diameter portion 305; the large-diameter portion 306 may be located only on the side of the small-diameter portion 305 that is opposite to the opening surface 35.

[0170] (Embodiment 2) As shown in Figure 9, the shape of the inner circumferential surface 301 of the flexible external gear 3 in the harmonic drive gear 1B according to this embodiment differs from the harmonic drive gear 1 according to Embodiment 1. Hereinafter, components similar to those in Embodiment 1 will be denoted by the same reference numerals and their descriptions will be omitted as appropriate. Figure 9 is a schematic cross-sectional view, similar to Figure 5, showing an enlarged view of the main parts in the area corresponding to Figure 1B.

[0171] In this embodiment, an intermediate section 307 is provided between the small-diameter section 305 and the large-diameter section 306, where the diameter gradually decreases toward the small-diameter section 305 in the tooth trace direction D1 of the external teeth 31. That is, in Embodiment 1, a stepped intermediate section 307 with a height difference of 5 μm or more and 30 μm or less is formed between the small-diameter section 305 and the large-diameter section 306, and the diameter (inner diameter) of the inner circumferential surface 301 changes discontinuously in the intermediate section 307. In contrast, in this embodiment, the diameter (inner diameter) of the inner circumferential surface 301 changes continuously in the intermediate section 307 between the small-diameter section 305 and the large-diameter section 306.

[0172] Specifically, for example, by making the intermediate portion 307 an inclined surface, similar to general tooth trace modification (crowning or relieving), the inner circumferential surface 301 of the flexible external gear 3 is machined to gradually recede from the outer ring 421 along the tooth trace direction D1. In particular, in the example shown in Figure 9, the diameter changes continuously from the first large diameter portion 306A to the small diameter portion 305, and further to the second large diameter portion 306B, so that the cross-section of the inner circumferential surface 301 becomes curved. Here, it is preferable that the length of the tooth trace direction D1, which is the sum of the small diameter portion 305 and the intermediate portion 307, is approximately equal to the width (dimension) of the outer ring 421.

[0173] This configuration makes it less likely for stress concentration to occur on the inner circumferential surface 301 of the flexible external gear 3, thus making it less likely for the flexible external gear 3 to be damaged.

[0174] As a modification of Embodiment 2, in the tooth trace direction D1, the intermediate portion 307 on one side (the side with the opening surface 35 or the side opposite to the opening surface 35) when viewed from the small diameter portion 305 may be configured to gradually decrease in diameter toward the small diameter portion 305. In this case, the diameter (inner diameter) of the inner circumferential surface 301 changes discontinuously in the other intermediate portion 307.

[0175] The configuration of Embodiment 2 (including modified versions) can be applied in appropriate combination with the configuration (including modified versions) described in Embodiment 1.

[0176] (summary) As described above, the wave drive gear (1, 1A, 1B) according to the first embodiment comprises 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 positioned inside the rigid internal gear (2). The wave generator (4) has a non-circular cam (41) that is rotationally driven around a rotation axis (Ax1), and a bearing (42) mounted on the outside of the cam (41). The wave generator (4) is positioned inside the flexible external gear (3) and causes the flexible external gear (3) to bend. The wave drive gear (1, 1A, 1B) deforms the flexible external gear (3) as the cam (41) rotates, engaging a portion of the external teeth (31) with a portion of the internal teeth (21), and 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 flexible external gear (3) and the rigid internal gear (2). The portion of the bearing (42) on the inner circumferential surface (301) of the flexible external gear (3) that faces the outer ring (421) includes a small-diameter portion (305) that is narrower than the outer ring (421) in the tooth trace direction (D1) of the external teeth (31), and a large-diameter portion (306) that is larger in diameter than the small-diameter portion (305).

[0177] In this embodiment, the inner circumferential surface (301) of the flexible external gear (3) contacts the outer ring (421) of the bearing (42) only at the small diameter portion (305) of the portion facing the outer ring (421), and does not contact the outer ring (421) at the large diameter portion (306). Furthermore, the small diameter portion (305) of the inner circumferential surface (301) of the flexible external gear (3), which is the portion that contacts the outer ring (421), is narrower than the outer ring (421) in the tooth trace direction (D1) of the external teeth (31). As a result, the outer ring (421) is less likely to contact both ends (corners) in the width direction with respect to the inner circumferential surface (301) of the flexible external gear (3), and the outer ring (421) makes surface contact with the small diameter portion (305) that is the portion that contacts the outer ring (421). Therefore, it is possible to provide a harmonic drive gear (1,1A,1B) that is less likely to experience a decrease in reliability because it is less likely to cause a step on the inner circumferential surface (301) of the flexible external gear (3) due to contact with the bearing (42).

[0178] In the second embodiment of the harmonic drive gear (1,1A,1B), the small diameter portion (305) is integrated with the flexible external gear (3) as in the first embodiment.

[0179] According to this embodiment, the positional accuracy of the small-diameter portion (305) can be improved, and the small-diameter portion (305) and the large-diameter portion (306) can be easily formed.

[0180] In the third embodiment of the harmonic drive gear (1,1A,1B), in the first or second embodiment, an intermediate portion (307) is provided between the small diameter portion (305) and the large diameter portion (306), which gradually decreases in diameter toward the small diameter portion (305) in the tooth trace direction (D1) of the external teeth (31).

[0181] According to this embodiment, stress concentration is less likely to occur on the inner circumferential surface (301) of the flexible external gear (3), and damage to the flexible external gear (3) is less likely to occur.

[0182] In the fourth embodiment of the harmonic drive gear (1, 1A, 1B), in any of the first to third embodiments, the large diameter portion (306) includes a first large diameter portion (306A) and a second large diameter portion (306B) located on both sides of the small diameter portion (305) in the tooth trace direction (D1) of the external teeth (31).

[0183] According to this embodiment, the occurrence of steps on the inner circumferential surface (301) of the flexible external gear (3) due to contact with the bearing (42) becomes less likely.

[0184] In the fifth embodiment of the harmonic drive gear (1,1A,1B), in any of the first to fourth embodiments, the outer ring (421) has higher hardness than the inner circumferential surface (301) of the flexible external gear (3).

[0185] According to this embodiment, the occurrence of steps on the inner circumferential surface (301) of the flexible external gear (3) due to contact with the bearing (42) becomes less likely.

[0186] In the sixth embodiment of the harmonic drive gear (1,1A,1B), in any of the first to fifth embodiments, the flexible external gear (3) is cylindrical with an opening surface (35) on one side in the tooth trace direction (D1) of the external teeth (31). The large diameter portion (306) is located at least on the opening surface (35) side relative to the small diameter portion (305).

[0187] According to this embodiment, contact between the inner circumferential surface of the flexible external gear (3) and the outer ring (421) can be suppressed on the opening surface (35) side, where contact with the outer ring (421) becomes particularly strong due to the elastic deformation of the flexible external gear (3).

[0188] In the harmonic drive gear (1,1A,1B) according to the seventh embodiment, in any of the first to sixth embodiments, there is a difference of 5 μm or more and 30 μm or less between the radius of the small diameter portion (305) and the radius of the large diameter portion (306).

[0189] According to this embodiment, the occurrence of steps on the inner circumferential surface (301) of the flexible external gear (3) due to contact with the bearing (42) becomes less likely.

[0190] In the wave drive gear according to the eighth embodiment (1,1A,1B), in any of the first to seventh embodiments, the dimension (L1) of the small diameter portion (305) in the tooth trace direction (D1) of the external teeth (31) is 1 / 2 or more of the diameter (φ2) of the rolling element (423) of the bearing (42).

[0191] According to this embodiment, the occurrence of steps on the inner circumferential surface (301) of the flexible external gear (3) due to contact with the bearing (42) becomes less likely.

[0192] The robot joint device (130) according to the ninth embodiment comprises a harmonic drive gear device (1, 1A, 1B) according to any of the first to eight embodiments, a first member (131) fixed to a rigid internal gear (2), and a second member (132) fixed to a flexible external gear (3).

[0193] According to this embodiment, it is possible to provide a robot joint device (130) that is less likely to experience a decrease in reliability because it is less likely to cause a step on the inner circumferential surface (301) of the flexible external gear (3) due to contact with the bearing (42).

[0194] The gear component according to the tenth embodiment is used as a flexible external gear (3) in a harmonic drive gear (1, 1A, 1B) according to any of the first to eight embodiments.

[0195] According to this embodiment, it is possible to provide a gear component that is less prone to a decrease in reliability because it is less likely for a step to occur on the inner circumferential surface (301) of the flexible external gear (3) due to contact with the bearing (42).

[0196] The configurations relating to the second to eighth aspects are not essential to the harmonic drive gear (1, 1A, 1B) and can be omitted as appropriate. [Explanation of Symbols]

[0197] 1,1A,1B Harmonic drive gear 2. Rigid internal gear 3. Flexible external gear (gear component) 4. Wave Generator 21 Inner teeth 31 External teeth 35 Opening surface 41 Cam 42 bearings 130 Robot joint devices 131 First Member 132 Second Member 301 Inner surface (of a flexible external gear) 305 Small diameter section 306 Large diameter section 306A First large diameter section 306B Second large diameter section 421 Outer ring 423 Rolling element Ax1 Rotation axis D1 tooth trace direction L1 (dimension of the small diameter section) φ2 (Diameter of rolling element)

Claims

1. An annular rigid internal gear having internal teeth, An annular flexible external gear having external teeth and positioned inside the rigid internal gear, The device comprises a non-circular cam that is rotationally driven around a rotation axis, and a wave generator having a bearing mounted on the outside of the cam, positioned inside the flexible external gear, and causing deflection in the flexible external gear, A harmonic drive gear device in which the flexible external gear is deformed as the cam rotates, a portion of the external teeth meshing with a portion of the internal teeth, and the flexible external gear rotates relative to the rigid internal gear in accordance with the difference in the number of teeth between the flexible external gear and the rigid internal gear, The portion of the inner circumferential surface of the flexible external gear facing the outer ring of the bearing includes a small-diameter portion that is narrower than the outer ring in the tooth trace direction of the external teeth, and a large-diameter portion that is larger in diameter than the small-diameter portion. The outer ring has higher hardness compared to the inner surface of the flexible external gear. The outer ring and the external teeth of the flexible external gear have through holes that penetrate radially. Harsh drive gear system.

2. The difference in hardness between the outer ring and the inner surface of the flexible external gear is between HV250 and HV370. The wave drive gear apparatus according to claim 1.

3. The large diameter portion includes a first large diameter portion and a second large diameter portion located on both sides of the small diameter portion in the tooth trace direction of the external tooth. The harmonic drive gear apparatus according to claim 1 or 2.

4. The aforementioned flexible external gear is cylindrical in shape, having an opening surface on one side in the tooth trace direction of the external teeth, The large-diameter portion is located at least on the opening surface side relative to the small-diameter portion. The harmonic drive gear apparatus according to claim 1 or 2.

5. There is a difference of 5 μm or more and 30 μm or less between the radius of the small diameter portion and the radius of the large diameter portion. The harmonic drive gear apparatus according to claim 1 or 2.

6. A harmonic drive gear apparatus according to claim 1 or 2, A first member fixed to the rigid internal gear, The system comprises a second member fixed to the aforementioned flexible external gear, Joint device for robots.

7. A flexible external gear used in the wave drive gear apparatus according to claim 1 or 2, Gear parts.

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