Robotic arm structure of robot and internally-meshing planetary gear device

Abstract

Embodiments of the present disclosure relate to the technical field of robots, and provide a robotic arm structure of a robot comprising a joint device for a robot, and an internally-meshing planetary gear device. The internally-meshing planetary gear device comprises: an internally toothed gear having internal teeth; a planetary gear having external teeth locally meshed with the internal teeth; and a plurality of eccentric shafts. The plurality of eccentric shafts are configured at positions where a rotation axis serving as an axis of the internally toothed gear offsets, and are synchronously driven by an input gear. In the internally-meshing planetary gear device, the planetary gear swings by means of the plurality of eccentric shafts, so that the planetary gear rotates about the rotation axis relative to the internally toothed gear. The number of teeth of the internal teeth and the number of teeth of the external teeth are both odd numbers, and the difference between the number of teeth of the internal teeth and the number of teeth of the external teeth is 2. In this way, damage originating from indentations generated between the external teeth and the internal teeth is less likely to progress.

Description

Robotic arm structure and internal meshing planetary gear mechanism

[0001] Cross-references to related applications

[0002] This application is based on and claims priority to Japanese Patent Application No. 2025-011149, filed on January 27, 2025, and Chinese Patent Application No. 202411836360.5, filed on December 12, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure generally relates to the field of robotics, and more particularly to a robotic arm structure including a robotic joint device and an internally meshing planetary gear device, the robotic joint device including the internally meshing planetary gear device. Background Technology

[0004] In Japanese Patent Application Publication No. 50-158764, an internal meshing planetary gear device (reducer) using a subcycloidal toothed gear as a planetary gear is known. In this internal meshing planetary gear device, the planetary gear (external gear) held by an eccentric wheel rotates eccentrically within an internal gear (internal gear) composed of fixed circular arc tooth profiles, and the planetary gear rotates in the opposite direction as the eccentric wheel rotates.

[0005] In the internal meshing planetary gear device described in the aforementioned patent literature, a subcycloidal gear is used as a planetary gear, where the innermost part of the subcycloidal curve overlapping the base circle after the rotating circle has rotated around the base circle multiple times and returned to the starting point is not set as an integer ratio to the radius of the base circle. In this case, the number of internal teeth of the internal gear and the number of external teeth of the planetary gear are both odd, and the difference between their number of teeth is "2".

[0006] The structure described in the aforementioned patent document is not a distribution type. In the so-called distribution type eccentric oscillating internal meshing planetary gear device, the structure in which both the number of teeth on the internal gear and the number of teeth on the external gear are odd, and the difference between their tooth numbers is set to "2", is not employed. Therefore, in a distribution type internal meshing planetary gear device, when damage (surface-starting point type peeling) occurs between the external and internal teeth, for example, starting from an indentation caused by the intrusion of foreign matter such as abrasive powder, a combination of meshing related to the growth of the surface-starting point occurs every time the planetary gear rotates once, potentially leading to faster damage progression.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 50-158764 Summary of the Invention

[0010] The purpose of this invention is to provide a robotic arm structure including a robotic joint device and an internal meshing planetary gear device, wherein damage originating from an indentation between the external and internal teeth is difficult to progress, the robotic joint device including the internal meshing planetary gear device.

[0011] One aspect of the present invention provides a robotic arm structure, comprising a robotic joint device, wherein the robotic joint device includes: an internal meshing planetary gear device, comprising: an internal gear having internal teeth; a planetary gear having external teeth partially meshing with the internal teeth; and a plurality of eccentric shafts disposed at positions offset from a rotation axis that serves as the axis of the internal gear, synchronously driven by an input gear, wherein the planetary gear is oscillated by the plurality of eccentric shafts, thereby causing the planetary gear to rotate relative to the internal gear about the rotation axis, wherein the number of teeth of the internal gear and the number of teeth of the external gear are both odd, and the difference between the number of teeth of the internal gear and the number of teeth of the external gear is 2; a first member fixed to the internal gear; and a second member that rotates relative to the first member as the planetary gear rotates relative to the internal gear.

[0012] One aspect of the present invention provides an internal meshing planetary gear device comprising: an internal gear having internal teeth; a planetary gear having external teeth that partially mesh with the internal teeth; and a plurality of eccentric shafts. The plurality of eccentric shafts are positioned offset from a rotational axis that serves as the axis of the internal gear and are synchronously driven by an input gear. In the internal meshing planetary gear device, the planetary gear is oscillated by the plurality of eccentric shafts, thereby causing the planetary gear to rotate relative to the internal gear about the rotational axis. Both the number of teeth on the internal gear and the number of teeth on the external gear are odd, and the difference between the number of teeth on the internal gear and the number of teeth on the external gear is 2.

[0013] One aspect of the present invention provides a robot joint device comprising: the internal meshing planetary gear assembly; a first member fixed to the internal gear; and a second member that rotates relative to the first member in conjunction with the relative rotation of the planetary gear relative to the internal gear.

[0014] Invention Effects

[0015] According to the present invention, a robotic arm structure including a robotic joint device and an internal meshing planetary gear device are provided, which are capable of preventing damage from progressing from an indentation generated between the external and internal teeth. The robotic joint device includes the internal meshing planetary gear device. Attached Figure Description

[0016] Figure 1 is a perspective view of the schematic structure of the actuator of the internal meshing planetary gear device, including the basic structure.

[0017] Figure 2 is a schematic exploded perspective view of the aforementioned internal meshing planetary gear device as seen from the input side of the rotating shaft.

[0018] Figure 3 is a schematic exploded perspective view of the aforementioned internal meshing planetary gear device as seen from the output side of the rotating shaft.

[0019] Figure 4 is a schematic cross-sectional view of the aforementioned internal meshing planetary gear device.

[0020] Figure 5 is a sectional view of the aforementioned internal meshing planetary gear device along line A1-A1 of Figure 4.

[0021] Figure 6 is a sectional view of the aforementioned internal meshing planetary gear device along line B1-B1 of Figure 4.

[0022] Figure 7 is a schematic diagram of an example of the subcycloid of the tooth profile curve of the external teeth of the planetary gear constituting the internal meshing planetary gear device of Embodiment 1.

[0023] Figure 8 is a schematic diagram of an example of the planetary gears in the aforementioned internal meshing planetary gear device.

[0024] Figure 9 is a schematic diagram of an example of the planetary gear and internal gear 2 of the above-described internal meshing planetary gear device.

[0025] Figure 10 is a schematic diagram of an example of the subcycloid of the tooth profile curve of the external teeth of the planetary gear in the internal meshing planetary gear device constituting the comparative example.

[0026] Figure 11 is a schematic diagram of an example of the planetary gears in the aforementioned internal meshing planetary gear device.

[0027] Figure 12 is a schematic diagram of a robot joint device using the aforementioned internal meshing planetary gear mechanism. Detailed Implementation

[0028] (Basic Structure)

[0029] (1) Summary

[0030] The following is a summary of the internal meshing planetary gear device 1 of this basic structure, with reference to Figures 1 to 4. The figures referenced in this invention are schematic diagrams, and the size and thickness ratios of the structural elements shown may not reflect actual dimensional ratios. For example, the tooth profile, size, and number of teeth of the internal teeth 21 and external teeth 31 in Figures 1 to 4 are merely schematic representations for illustrative purposes, and their intent is not limited to the shapes shown in the figures.

[0031] The internal meshing planetary gear assembly 1 (hereinafter also simply referred to as "gear assembly 1") of this basic structure is a gear assembly including an internal gear 2 and a planetary gear 3. In this gear assembly 1, the planetary gear 3 is arranged inside the annular internal gear 2 and oscillated, thereby causing the planetary gear 3 to rotate relative to the internal gear 2. In addition, the internal meshing planetary gear assembly 1 also includes a bearing member 6, which has an outer ring 62 and an inner ring 61. The inner ring 61 is arranged inside the outer ring 62 and is supported so as to be able to rotate relative to the outer ring 62. In particular, the gear assembly 1 of this basic structure is a type of eccentric oscillating internal meshing planetary gear assembly called a distribution type.

[0032] As shown in Figures 1 to 4, the gear device 1 of this basic structure includes multiple (three in the basic structure) crankshafts (eccentric shafts) 7A, 7B, and 7C disposed at positions offset from the axis (rotation shaft Ax1) of the internal gear 2. Further, the gear device 1 includes an input shaft 500 disposed on the axis (rotation shaft Ax1) of the internal gear 2, centered on the rotation shaft Ax1, and an input gear 501 integrally formed with the input shaft 500. Crankshaft gears 502A, 502B, and 502C are respectively splined to the multiple crankshafts 7A, 7B, and 7C. These multiple (three in the basic structure) crankshaft gears 502A, 502B, and 502C are arranged to mesh with the input gear 501. Therefore, when the input shaft 500 is driven, the gear device 1 synchronously drives the crankshafts 7A, 7B, and 7C using the input gear 501, thereby causing the planetary gear 3 to oscillate.

[0033] The internal gear 2 has internal teeth 21 and is fixed to the outer ring 62. Specifically, in this basic structure, the internal gear 2 has an annular gear body 22 and multiple pins 23. The multiple pins 23 are held in a rotatable state on the inner circumferential surface 221 of the gear body 22, thus forming the internal teeth 21. The planetary gear 3 has external teeth 31 that partially mesh with the internal teeth 21. That is, inside the internal gear 2, the planetary gear 3 is tangent to the internal gear 2, becoming a part of the external teeth 31 meshing with a part of the internal teeth 21. In this state, when multiple crankshafts 7A, 7B, and 7C are driven, the planetary gear 3 oscillates, and the meshing position of the internal teeth 21 and external teeth 31 moves along the circumferential direction of the internal gear 2, generating a relative rotation between the two gears (internal gear 2 and planetary gear 3) corresponding to the difference in the number of teeth between the planetary gear 3 and the internal gear 2. Here, if the internal gear 2 is fixed, the planetary gear 3 rotates (rotates) along with the relative rotation of the two gears. As a result, a rotational output that is reduced at a relatively high reduction ratio can be obtained from planetary gear 3, corresponding to the difference in the number of teeth between the two gears.

[0034] This gear device 1 is used in such a way that the rotation of the planetary gear 3, corresponding to its rotational component, is achieved by rotating a pair of supports 18 and 19 that are fixed relative to the inner ring 61 of the bearing member 6 via an integral or embedded mechanism. Thus, the gear device 1 functions as a gear device with a relatively high reduction ratio, using the input shaft 500 as the input side and the pair of supports 18 and 19 as the output side. Therefore, in this basic structure of the gear device 1, multiple crankshafts 7A, 7B, and 7C are supported by the pair of supports 18 and 19 in order to transmit the rotation of the planetary gear 3, corresponding to its rotational component, to the pair of supports 18 and 19. The pair of supports 18 and 19 are arranged on both sides of the axial direction (along the direction of the rotation axis Ax1) of the planetary gear 3 and rotatably support each crankshaft 7A, 7B, and 7C.

[0035] Here, multiple crankshafts 7A, 7B, and 7C, each inserted into a plurality of openings 33 formed in the planetary gear 3, rotate relative to the internal gear 2 as the planetary gear 3 rotates. Furthermore, each crankshaft 7A, 7B, and 7C has a central shaft 71 and an eccentric portion 72 eccentric to the central shaft 71. A pair of supports 18 and 19 rotatably support the central shaft 71 of each crankshaft 7A, 7B, and 7C, and the eccentric portion 72 of each crankshaft 7A, 7B, and 7C is inserted into the openings 33 of the planetary gear 3. When each crankshaft 7A, 7B, and 7C rotates around its respective central shaft 71, each eccentric portion 72 rotates eccentrically relative to its respective central shaft 71 (eccentric motion). Accompanying this, the planetary gear 3 oscillates. Through the oscillation of the planetary gear 3, the planetary gear 3 partially meshes with the internal gear 2 and rotates relative to the internal gear 2. As a result, planetary gear 3 rotates on its own central axis while revolving within internal gear 2 in a manner revolving around the rotation axis Ax1. Along with the rotation of planetary gear 3, each crankshaft 7A, 7B, and 7C revolves around the rotation axis Ax1, and the supports 18 and 19 of the shaft center 71 supporting each crankshaft 7A, 7B, and 7C rotate on their own axes in accordance with the revolution of each crankshaft 7A, 7B, and 7C. In this way, through multiple crankshafts 7A, 7B, and 7C, the rotation component (rotation component) of planetary gear 3, excluding the oscillation component (revolution component), is transmitted to a pair of supports 18 and 19.

[0036] Furthermore, as shown in Figure 1, the gear assembly 1 of this basic structure, together with the drive source 101, constitutes the actuator 100. In other words, the actuator 100 of this basic structure includes the gear assembly 1 and the drive source 101. The drive source 101 generates a driving force for oscillating the planetary gear 3. Specifically, the drive source 101 causes the input shaft 500 to rotate about the rotation axis Ax1, thereby causing the planetary gear 3 to oscillate.

[0037] (2) Definition

[0038] The term "ring-shaped" as used in this invention refers to a shape that forms a circle (ring) enclosing a space (region) on the inside when viewed from above, and is not limited to a circular shape (ring-shaped) that is perfectly round when viewed from above. For example, it can also be an elliptical shape or a polygonal shape. Furthermore, for example, even a shape with a bottom, such as a cup, is included in the term "ring-shaped" as long as its peripheral walls are ring-shaped.

[0039] In this invention, "revolution" refers to an object revolving around an axis of rotation other than the central axis passing through the object's center (center of gravity). When an object revolves, its center moves along a revolution path centered on the axis of rotation. Therefore, for example, when an object rotates around an eccentric axis parallel to the central axis passing through its center (center of gravity), the object revolves around the eccentric axis. As an example, planetary gear 3 revolves within internal gear 2 by oscillating and rotating around the axis of rotation Ax1.

[0040] Furthermore, in some publications, one side of the rotating shaft Ax1 (the left side of Figure 4) is referred to as the "output side," and the other side of the rotating shaft Ax1 (the right side of Figure 4) is referred to as the "input side." In the example of Figure 4, rotation is imparted to the input shaft 500 from the "input side" of the rotating shaft Ax1, and rotation is taken out from the "output side" of the rotating shaft Ax1 for the pair of supports 18 and 19. However, "input side" and "output side" are merely labels used for illustrative purposes, and their purpose is not limited to the positional relationship of the input and output as observed from the gear device 1.

[0041] In this invention, the term "rotation axis" refers to a virtual axis (straight line) that serves as the center of rotational motion of the rotating body. In other words, rotation axis Ax1 is a virtual axis without a physical form. The input axis 500 rotates around rotation axis Ax1.

[0042] In this invention, "internal teeth" and "external teeth" refer to a collection (group) of multiple "teeth" rather than a single "teeth". That is, the internal teeth 21 of the internal gear 2 are composed of a collection of multiple teeth disposed on the inner circumferential surface 221 of the internal gear 2 (gear body 22). Similarly, the external teeth 31 of the planetary gear 3 are composed of a collection of multiple teeth disposed on the outer circumferential surface of the planetary gear 3.

[0043] (3) Structure

[0044] The detailed structure of the internal meshing planetary gear device 1 of this basic structure will be described below with reference to Figures 1 to 6.

[0045] Figure 1 is a perspective view showing the schematic structure of the actuator 100 including the gear mechanism 1. In Figure 1, the drive source 101 is schematically shown. Figure 2 is a schematic exploded perspective view of the gear mechanism 1 viewed from the input side of the rotating shaft Ax1. Figure 3 is a schematic exploded perspective view of the gear mechanism 1 viewed from the output side of the rotating shaft Ax1. Figure 4 is a schematic sectional view of the gear mechanism 1. Figure 5 is a sectional view along line A1-A1 of Figure 4. Figure 6 is a sectional view along line B1-B1 of Figure 4. In Figures 5 and 6, although the sections are also cross-sections of components other than the crankshafts 7A, 7B, and 7C, the section lines are omitted.

[0046] (3.1) Overall Structure

[0047] As shown in Figures 1 to 4, the gear assembly 1 of this basic structure includes an internal gear 2, a planetary gear 3, a bearing component 6, multiple crankshafts 7A, 7B, and 7C, a pair of supports 18 and 19, and an input shaft 500. Additionally, in this basic structure, the gear assembly 1 also includes an input gear 501, multiple crankshaft gears 502A, 502B, and 502C, a pair of rolling bearings 41 and 42, an eccentric bearing 5, and a housing 10. In this basic structure, the internal gear 2, planetary gear 3, multiple crankshafts 7A, 7B, and 7C, and the pair of supports 18 and 19, which are structural elements of the gear assembly 1, are made of stainless steel, cast iron, carbon steel for mechanical structures, chromium-molybdenum steel, phosphor bronze, or aluminum bronze, or light metals such as aluminum or titanium. The metals mentioned here (including light metals) include metals that have undergone surface treatments such as nitriding.

[0048] Furthermore, in this basic structure, as an example of gear device 1, an internal meshing planetary gear reduction device with a subcycloidal tooth profile is illustrated. That is, gear device 1 of this basic structure includes an internal meshing planetary gear 3 having a subcycloidal curved tooth profile.

[0049] Furthermore, in this basic structure, as an example, the gear device 1 is used with the gear body 22 of the internal gear 2 and the outer ring 62 of the bearing member 6 fixed to a fixed member such as the housing 10. Thus, as the internal gear 2 and the planetary gear 3 rotate relative to each other, the planetary gear 3 rotates relative to the fixed member (such as the housing 10).

[0050] Furthermore, in this basic structure, when the gear device 1 is used in the actuator 100, by applying a rotational force as input to the input shaft 500, a rotational force as output is extracted from a pair of supports 18, 19 integrated with the inner ring 61 of the bearing member 6. In other words, the gear device 1 operates with the rotation of the input shaft 500 as input rotation and the rotation of the pair of supports 18, 19 integrated with the inner ring 61 as output rotation. Thus, in the gear device 1, an output rotation that is reduced at a relatively high reduction ratio relative to the input rotation can be obtained.

[0051] The drive source 101 is a power source such as an electric motor. The power generated by the drive source 101 is transmitted to the input shaft 500 in the gear assembly 1. Specifically, the drive source 101 is connected to the input shaft 500, and the power generated by the drive source 101 is transmitted to the input shaft 500. Thus, the drive source 101 can rotate the input shaft 500.

[0052] Furthermore, in the gear device 1 of this basic structure, as shown in FIG4, the rotational shaft Ax1 on the input side and the rotational shaft Ax1 on the output side are on the same straight line. In other words, the rotational shaft Ax1 on the input side and the rotational shaft Ax1 on the output side are coaxial. Here, the rotational shaft Ax1 on the input side is the rotation center of the input shaft 500 to which the input rotation is imparted, and the rotational shaft Ax1 on the output side is the rotation center of the inner ring 61 (and the pair of supports 18, 19) that generate the output rotation. That is to say, in the gear device 1, it is possible to obtain an output rotation that is reduced in speed by a relatively high reduction ratio by rotating coaxially relative to the input.

[0053] As shown in Figures 5 and 6, the internal gear 2 is an annular component with internal teeth 21. In this basic structure, the internal gear 2 has an annular shape, at least its inner circumferential surface being a perfect circle when viewed from above. Internal teeth 21 are formed along the circumferential direction of the annular internal gear 2 on its inner circumferential surface. All teeth constituting the internal teeth 21 are of the same shape and are evenly spaced throughout the entire circumferential region of the inner circumferential surface of the internal gear 2. That is, the pitch circle of the internal teeth 21 is a perfect circle when viewed from above. The center of the pitch circle of the internal teeth 21 is located on the rotation axis Ax1. Furthermore, the internal gear 2 has a predetermined thickness along the direction of the rotation axis Ax1. The tooth directions of the internal teeth 21 are all parallel to the rotation axis Ax1. The dimension of the internal teeth 21 in the tooth direction is slightly smaller than that in the thickness direction of the internal gear 2.

[0054] Here, as described above, the internal gear 2 has an annular (ring-shaped) gear body 22 and multiple pins 23. The multiple pins 23 are held in a rotatable state on the inner circumferential surface 221 of the gear body 22, forming the internal gear 21. In other words, the multiple pins 23 function as multiple teeth constituting the internal gear 21. Specifically, as shown in FIG2, multiple inner circumferential grooves 223 are formed on the entire circumferential area of ​​the inner circumferential surface 221 of the gear body 22. All of the multiple inner circumferential grooves 223 are of the same shape and are arranged at equal intervals. The multiple inner circumferential grooves 223 are all parallel to the rotation axis Ax1 and are formed along the entire thickness direction of the gear body 22. The multiple pins 23 are combined with the gear body 22 in a manner that they are embedded in the multiple inner circumferential grooves 223. Each of the multiple pins 23 is held in a state where it can rotate within the inner circumferential groove 223. Furthermore, the gear body 22 (together with the outer ring 62) is fixed to the housing 10. Furthermore, a plurality of fixing holes 222 for fixing are formed in the gear body 22 (see Figure 5).

[0055] As shown in Figures 5 and 6, the planetary gear 3 is an annular component with external teeth 31. In this basic structure, the planetary gear 3 has an annular shape, at least its outer circumferential surface being a perfect circle when viewed from above. External teeth 31 are formed on the outer circumferential surface of the annular planetary gear 3 along the circumferential direction of the planetary gear 3. All the teeth constituting the external teeth 31 are of the same shape and are evenly spaced throughout the entire circumferential region of the outer circumferential surface of the planetary gear 3. That is, the pitch circle of the external teeth 31 is a perfect circle when viewed from above. Furthermore, the planetary gear 3 has a predetermined thickness along the direction of the rotation axis Ax1. The external teeth 31 are formed along the entire length of the thickness direction of the planetary gear 3. The tooth directions of the external teeth 31 are all parallel to the rotation axis Ax1. Unlike the internal gear 2, in the planetary gear 3, the external teeth 31 and the main body of the planetary gear 3 are integrally formed from a single metal component.

[0056] Furthermore, the gear assembly 1 of this basic structure includes a plurality of planetary gears 3. Specifically, the gear assembly 1 includes two planetary gears 3: a first planetary gear 301 and a second planetary gear 302. The two planetary gears 3 are arranged opposite each other in a direction parallel to the rotation axis Ax1. That is, the planetary gears 3 comprise a first planetary gear 301 and a second planetary gear 302 arranged in a direction (axial direction) parallel to the rotation axis Ax1. The shapes of the first planetary gear 301 and the second planetary gear 302 are themselves generic.

[0057] These two planetary gears 3 (first planetary gear 301 and second planetary gear 302) are arranged about the rotation axis Ax1 with a phase difference of 180 degrees. In the example of Figure 4, the center (center of the pitch circle of the external tooth 31) C1 of the first planetary gear 301, located on the input side of the rotation axis Ax1 (right side of Figure 4), is offset (offset) relative to the rotation axis Ax1 upwards in the figure. On the other hand, the center (center of the pitch circle of the external tooth 31) C2 of the second planetary gear 302, located on the output side of the rotation axis Ax1 (left side of Figure 4), is offset (offset) relative to the rotation axis Ax1 downwards in the figure. Here, the distance ΔL1 between the rotation axis Ax1 and the center C1 is the eccentricity of the first planetary gear 301 relative to the rotation axis Ax1, and the distance ΔL2 between the rotation axis Ax1 and the center C2 is the eccentricity of the second planetary gear 302 relative to the rotation axis Ax1. In this way, multiple planetary gears 3 are evenly arranged in the circumferential direction centered on the rotation axis Ax1, thereby achieving a balance of weight and load among the multiple planetary gears 3.

[0058] In the first planetary gear 301 and the second planetary gear 302, their centers C1 and C2 are rotationally symmetrical about 180 degrees relative to the rotation axis Ax1. In this basic structure, although the orientations of the eccentricities ΔL1 and ΔL2 observed from the rotation axis Ax1 are opposite, their absolute values ​​are the same.

[0059] More specifically, each crankshaft 7A, 7B, and 7C has two eccentric portions 72 relative to a central shaft portion 71. The eccentricity ΔL0 (refer to Figures 5 and 6) of the center C0 of these two eccentric portions 72 from the center (shaft Ax2) of the central shaft portion 71 is the same as the eccentricity ΔL1 and ΔL2 of the first planetary gear 301 and the second planetary gear 302 relative to the rotation axis Ax1, respectively. The shapes of the multiple crankshafts 7A, 7B, and 7C are inherently common. The shapes of the multiple crankshaft gears 502A, 502B, and 502C are also inherently common.

[0060] Furthermore, a pair of supports 18 and 19 are arranged on both sides of the first planetary gear 301 and the second planetary gear 302 in the direction parallel to the rotation axis Ax1 (axial direction). Distinguishing between the two supports 18 and 19, the support 18 located on the input side of the rotation axis Ax1 (right side in Figure 4) is referred to as the "input side support 18," and the support 19 located on the output side of the rotation axis Ax1 (left side in Figure 4) is referred to as the "output side support 19." The two ends of each crankshaft 7A, 7B, and 7C are held in place by the pair of supports 18 and 19 via rolling bearings 41 and 42. That is, each crankshaft 7A, 7B, and 7C is held in a rotatable state relative to the planetary gear 3 on both sides in the direction parallel to the rotation axis Ax1 (axial direction) by the input side support 18 and the output side support 19.

[0061] An eccentric bearing 5 is fitted to the eccentric portion 72 of each crankshaft 7A, 7B, and 7C. Three openings 33 corresponding to the three crankshafts 7A, 7B, and 7C are formed on the first planetary gear 301 and the second planetary gear 302, respectively. An eccentric bearing 5 is housed in each opening 33. In other words, eccentric bearings 5 ​​are mounted on the first planetary gear 301 and the second planetary gear 302, and each crankshaft 7A, 7B, and 7C is inserted into the eccentric bearing 5, thereby combining the eccentric bearing 5 and each crankshaft 7A, 7B, and 7C with the planetary gear 3. With the planetary gear 3 combined with the eccentric bearing 5 and the crankshafts 7A, 7B, and 7C, when each crankshaft 7A, 7B, and 7C rotates, the planetary gear 3 oscillates around the rotation axis Ax1.

[0062] Based on the structure described above, by applying a rotational force as input to the input shaft 500, the input shaft 500 rotates around the rotation axis Ax1. This rotational force is then distributed from the input gear 501 to multiple crankshafts 7A, 7B, and 7C. In other words, when the input gear 501 rotates, the three crankshaft gears 502A, 502B, and 502C that mesh with it rotate in the same direction at the same speed. Since crankshafts 7A, 7B, and 7C are splined to each of the crankshaft gears 502A, 502B, and 502C, the three crankshafts 7A, 7B, and 7C rotate in the same direction at the same speed while being reduced in speed by a gear ratio relative to the input gear 501 and the crankshaft gears 502A, 502B, and 502C. As a result, the three eccentric portions 72 of the three crankshafts 7A, 7B, and 7C, located at the same position on the input side of the rotating shaft Ax1, rotate synchronously, causing the first planetary gear 301 to oscillate. Furthermore, the three eccentric portions 72 of the three crankshafts 7A, 7B, and 7C, located at the same position on the output side of the rotating shaft Ax1, rotate synchronously, causing the second planetary gear 302 to oscillate.

[0063] Figures 5 and 6 show the state of the first planetary gear 301 and the second planetary gear 302 at a certain moment. Figure 5 is a cross-sectional view along line A1-A1 of Figure 4, showing the first planetary gear 301. Figure 6 is a cross-sectional view along line B1-B1 of Figure 4, showing the second planetary gear 302. As shown in Figures 5 and 6, the centers C1 and C2 of the first planetary gear 301 and the second planetary gear 302 are located at approximately 180 degrees rotationally symmetrical relative to the rotation axis Ax1. In this basic structure, although the orientations of the eccentricities ΔL1 and ΔL2 observed from the rotation axis Ax1 are opposite, their absolute values ​​are approximately the same (both are eccentricities ΔL0). According to the above structure, the shaft center 71 rotates (rotates) around the shaft center Ax2, thereby causing the first planetary gear 301 and the second planetary gear 302 to rotate (eccentrically move) around the rotation axis Ax1 with an approximately 180-degree phase difference. Furthermore, the multiple planetary gears 3 are arranged approximately equally in the circumferential direction centered on the rotation axis Ax1, thereby achieving a balance of weight and load among the multiple planetary gears 3.

[0064] The planetary gears 3 (first planetary gear 301 and second planetary gear 302) configured in this way are positioned inside the internal gear 2. Viewed from above, the planetary gear 3 is one size smaller than the internal gear 2, and when combined with the internal gear 2, the planetary gear 3 can oscillate inside the internal gear 2. At this time, external teeth 31 are formed on the outer circumferential surface of the planetary gear 3, and internal teeth 21 are formed on the inner circumferential surface of the internal gear 2. Therefore, with the planetary gear 3 positioned inside the internal gear 2, the external teeth 31 and the internal teeth 21 are opposite each other.

[0065] Furthermore, the pitch circle of the external tooth 31 is one rotation smaller than that of the internal tooth 21. Also, when the first planetary gear 301 is internally tangent to the internal gear 2, the center C1 of the pitch circle of the external tooth 31 of the first planetary gear 301 is located at a distance ΔL1 from the center of the pitch circle of the internal tooth 21 (rotation axis Ax1). Similarly, when the second planetary gear 302 is internally tangent to the internal gear 2, the center C2 of the pitch circle of the external tooth 31 of the second planetary gear 302 is located at a distance ΔL2 from the center of the pitch circle of the internal tooth 21 (rotation axis Ax1).

[0066] Therefore, in either the first planetary gear 301 or the second planetary gear 302, at least a portion of the external tooth 31 and the internal tooth 21 face each other with a clearance. If the difference in the number of teeth between the external tooth 31 and the internal tooth 21 is greater than 2, they will not mesh together in the circumferential direction. However, the planetary gear 3 oscillates (revolves) around the rotation axis Ax1 inside the internal gear 2, so the external tooth 31 and the internal tooth 21 mesh partially. That is, as shown in Figures 5 and 6, by the oscillation of the planetary gear 3 (first planetary gear 301 and second planetary gear 302) around the rotation axis Ax1, a portion of the teeth constituting the external tooth 31 meshes with a portion of the teeth constituting the internal tooth 21. As a result, in the gear assembly 1, a portion of the external tooth 31 can mesh with a portion of the internal tooth 21.

[0067] Here, the number of teeth of the internal gear 21 in the internal gear 2 is N more than the number of teeth of the external gear 31 in the planetary gear 3 (N is a positive integer). In this basic structure, as an example, N is "2", and the number of teeth of the planetary gear 3 (external teeth 31) is "2" less than the number of teeth of the internal gear 2 (internal teeth 21). This difference in the number of teeth between the planetary gear 3 and the internal gear 2 defines the reduction ratio of the output rotation relative to the input rotation in the gear unit 1.

[0068] Furthermore, in this basic structure, as an example, the combined thickness of the first planetary gear 301 and the second planetary gear 302 is smaller than the thickness of the gear body 22 in the internal gear 2. Further, the dimension of the tooth direction (parallel to the rotation axis Ax1) of the external teeth 31 of the combined first planetary gear 301 and the second planetary gear 302 is smaller than the dimension of the tooth direction (parallel to the rotation axis Ax1) of the internal teeth 21. In other words, in the direction parallel to the rotation axis Ax1, the external teeth 31 of the first planetary gear 301 and the second planetary gear 302 are contained within the tooth direction of the internal teeth 21.

[0069] Here, the first planetary gear 301 and the second planetary gear 302 are internally meshed with the internal gear 2. Therefore, with each oscillation of the first planetary gear 301 and the second planetary gear 302, the first planetary gear 301 and the second planetary gear 302 experience a circumferential phase deviation relative to the internal gear 2 (the difference in the number of teeth between the internal teeth 21 and the external teeth 31), and rotate. Through this rotation, the first planetary gear 301 and the second planetary gear 302 partially mesh with the internal teeth 21 of the internal gear 2 while revolving around the inner circumference of the internal gear 2 (i.e., revolving around the rotation axis Ax1). Accompanying the revolution of the planetary gear 3, the crankshafts 7A, 7B, and 7C inserted into the opening 33 of the planetary gear 3 revolve around the rotation axis Ax1. In this way, the revolution of the planetary gear 3 is transmitted to a pair of supports 18 and 19 via the multiple crankshafts 7A, 7B, and 7C. Thus, a pair of supports 18 and 19 can rotate relative to the gear body (and the integrated housing 10) with the rotation axis Ax1 as the center.

[0070] In summary, the gear mechanism 1 of this basic structure uses multiple crankshafts 7A, 7B, and 7C, positioned offset from the pivot Ax1, to oscillate the planetary gear 3, and utilizes the oscillation of the planetary gear 3 to obtain rotational output. That is, in the gear mechanism 1, when the planetary gear 3 oscillates, the meshing position of the internal gear 21 and the external gear 31 moves along the circumferential direction of the internal gear 2, generating a relative rotation between the two gears (internal gear 2 and planetary gear 3) corresponding to the difference in the number of teeth between the planetary gear 3 and the internal gear 2. Here, if the internal gear 2 is fixed, the planetary gear 3 rotates (spins) along with the relative rotation of the two gears. As a result, a rotational output that is reduced in speed at a relatively high reduction ratio, corresponding to the difference in the number of teeth between the two gears, can be obtained from the planetary gear 3.

[0071] The bearing component 6 has an outer ring 62 and an inner ring 61 and is used to extract the output of the gear device 1 as the rotation of the inner ring 61 relative to the outer ring 62. In addition to the outer ring 62 and the inner ring 61, the bearing component 6 also has a plurality of rolling elements 63 (see Figure 4). Both the outer ring 62 and the inner ring 61 are annular components. Both the outer ring 62 and the inner ring 61 are circular when viewed from above. The inner ring 61 is smaller than the outer ring 62 and is positioned inside the outer ring 62. Here, the inner diameter of the outer ring 62 is larger than the outer diameter of the inner ring 61, thus creating a gap between the inner circumferential surface of the outer ring 62 and the outer circumferential surface of the inner ring 61.

[0072] Multiple rolling elements 63 are disposed in the gap between the outer ring 62 and the inner ring 61. The multiple rolling elements 63 are arranged along the circumferential direction of the outer ring 62. All of the multiple rolling elements 63 are metal parts of the same shape and are evenly spaced throughout the entire circumferential area of ​​the outer ring 62.

[0073] More specifically, the gear assembly 1 of this basic structure includes a first main bearing 601 and a second main bearing 602, which respectively serve as bearing members 6. That is, the gear assembly 1 includes a pair of bearing members 6 consisting of the first main bearing 601 and the second main bearing 602. Specifically, as shown in FIG4, the first main bearing 601 is arranged on the input side of the rotating shaft Ax1 (right side of FIG4) when viewed from the planetary gear 3, and the second main bearing 602 is arranged on the output side of the rotating shaft Ax1 (left side of FIG4) when viewed from the planetary gear 3. The pair of bearing members 6, through the first main bearing 601 and the second main bearing 602, are configured to withstand radial loads, thrust loads (along the direction of the rotating shaft Ax1), and bending forces (bending moment loads) on the rotating shaft Ax1.

[0074] Here, the first bearing member 601 and the second bearing member 602 are positioned opposite each other in the direction parallel to the rotation axis Ax1 relative to the planetary gear 3 (axial direction). That is, the bearing member 6 is a "combined angular ball bearing" that combines multiple (here, two) angular ball bearings. Here, as an example, the first bearing member 601 and the second bearing member 602 are "back-mounted" types that bear loads in the thrust direction (along the rotation axis Ax1) with their respective inner rings 61 approaching each other. Furthermore, in the gear assembly 1, the first bearing member 601 and the second bearing member 602 are combined to apply appropriate preload to the inner rings 61 by fastening their respective inner rings 61 towards each other.

[0075] Furthermore, in the gear assembly 1 of this basic structure, the input-side bracket 18 and the output-side bracket 19 are arranged on opposite sides of the planetary gear 3 in a direction parallel to the rotation axis Ax1, and are joined together by passing through the bracket hole 34 of the planetary gear 3 (see Figure 4). Specifically, as shown in Figure 4, the input-side bracket 18 is arranged on the input side of the rotation axis Ax1 (right side of Figure 4) when viewed from the planetary gear 3, and the output-side bracket 19 is arranged on the output side of the rotation axis Ax1 (left side of Figure 4) when viewed from the planetary gear 3. The inner ring 61 of the bearing member 6 (each of the first bearing member 601 and the second bearing member 602) is fixed to the input-side bracket 18 and the output-side bracket 19. In this basic structure, as an example, the inner ring of the first bearing member 601 is seamlessly integrated with the input-side bracket 18. Similarly, the inner ring of the second bearing member 602 is seamlessly integrated with the output-side bracket 19.

[0076] The output-side bracket 19 has a plurality of (three in one example) bracket pins 191 (see Figure 2) protruding from one surface of the output-side bracket 19 toward the input side of the rotation shaft Ax1. These bracket pins 191 pass through a plurality of (three in one example) bracket holes 34 formed in the planetary gear 3, and the front ends of the bracket pins 191 are fixed relative to the input-side bracket 18 by bracket bolts 192 (see Figure 7). Here, a gap is ensured between the bracket pins 191 and the inner circumferential surface of the bracket holes 34, allowing the bracket pins 191 to move within the bracket holes 34, that is, to move relative to the center of the bracket holes 34. Therefore, when the planetary gear 3 oscillates, the bracket pins 191 do not contact the inner circumferential surface of the bracket holes 34.

[0077] With the above structure, the gear device 1 is used in such a way that the rotation of the planetary gear 3, corresponding to its rotational component, is taken out as the rotation of the input-side bracket 18 and the output-side bracket 19, which are integrated with the inner ring 61 of the bearing member 6. That is, in this basic structure, the relative rotation between the planetary gear 3 and the internal gear 2 is taken out from the input-side bracket 18 and the output-side bracket 19. In this basic structure, as an example, the gear device 1 is used with the outer ring 62 of the bearing member 6 (see Figure 4) fixed to the housing 10, which is a fixed member. That is, the planetary gear 3 is connected to the input-side bracket 18 and the output-side bracket 19, which are rotating members, by means of multiple crankshafts 7A, 7B, and 7C, and the gear body 22 is fixed to the fixed member, so the relative rotation between the planetary gear 3 and the internal gear 2 is taken out from the rotating members (input-side bracket 18 and output-side bracket 19). In other words, in this basic structure, when the planetary gear 3 is configured to rotate relative to the gear body 22, the rotational force of the input-side bracket 18 and the output-side bracket 19 is taken out as the output.

[0078] Furthermore, in this basic structure, the housing 10 and the gear body 22 of the internal gear 2 are seamlessly integrated. That is, in the direction parallel to the rotation axis Ax1, the gear body 22, as a fixing member, is seamlessly and continuously arranged with the housing 10.

[0079] More specifically, the housing 10 is cylindrical and forms the outer contour of the gear assembly 1. In this basic structure, the central axis of the cylindrical housing 10 is aligned with the rotation axis Ax1. That is, at least the outer circumferential surface of the housing 10, when viewed from above (from the axial direction), is a perfect circle centered on the rotation axis Ax1. The housing 10 is formed as a cylinder with openings at both axial ends. Here, the housing 10 is seamlessly integrated with the gear body 22 of the internal gear 2, so that the housing 10 and the gear body 22 are treated as a single component. Therefore, the inner circumferential surface of the housing 10 includes the inner circumferential surface 221 of the gear body 22. Furthermore, the outer ring 62 of the bearing member 6 is fixed to the housing 10. That is, when viewed from the gear body 22 on the inner circumferential surface of the housing 10, the outer ring 62 of the first bearing member 601 is fixed to the input side of the rotation axis Ax1 (right side of FIG. 4) by embedding. On the other hand, viewed from the gear body 22 in the inner circumferential surface of the housing 10, the outer ring 62 of the second bearing member 602 is fixed to the output side of the rotating shaft Ax1 by embedding (left side of FIG4).

[0080] Furthermore, the input side (right side of Figure 4) end face of the rotation shaft Ax1 of the housing 10 is blocked by the input side bracket 18, and the output side (left side of Figure 4) end face of the rotation shaft Ax1 of the housing 10 is blocked by the output side bracket 19. Therefore, as shown in Figure 4, the space surrounded by the housing 10, the input side bracket 18, and the output side bracket 19 houses components such as planetary gears 3 (first planetary gear 301 and second planetary gear 302), multiple pins 23, and eccentric bearings 5.

[0081] Multiple crankshafts 7A, 7B, and 7C (in a basic structure of three) each have a central shaft portion 71 and two eccentric portions 72. The central shaft portion 71 is cylindrical, with at least its outer circumferential surface being perfectly circular when viewed from above. The shaft center Ax2, which serves as the center of the central shaft portion 71, is parallel to the rotation axis Ax1. The shaft centers Ax2 of the multiple crankshafts 7A, 7B, and 7C are arranged at equal intervals in the circumferential direction on a virtual circle centered on the rotation axis Ax1. Each eccentric portion 72 is disc-shaped, with at least its outer circumferential surface being perfectly circular when viewed from below. The center (central axis) C0 of each eccentric portion 72 is parallel to the rotation axis Ax1 and is positioned radially offset from the rotation axis Ax1. Here, the distance ΔL0 between the shaft center Ax2 and the center C0 (refer to Figures 5 and 6) is the eccentricity relative to the central shaft portion 71. The eccentric portion 72 is a flange shape that protrudes from the outer circumference of the shaft portion 71 at its center along the longitudinal direction (axial direction). According to the above structure, for each crankshaft 7A, 7B, 7C, the eccentric portion 72 performs eccentric motion by rotating the shaft portion 71 around the shaft center Ax2.

[0082] In this basic structure, the central shaft 71 and the two eccentric shafts 72 are integrally formed from a single metal component, thereby achieving seamless crankshafts 7A, 7B, and 7C. These crankshafts 7A, 7B, and 7C, in this shape, are combined with the eccentric bearings 5 ​​in the planetary gear 3. Therefore, with the planetary gear 3 assembled with the eccentric bearings 5 ​​and the crankshafts 7A, 7B, and 7C, the planetary gear 3 oscillates around the rotation axis Ax1 when the crankshafts 7A, 7B, and 7C rotate.

[0083] The eccentric bearing 5 is a component having multiple rolling elements 51 (see Figure 4) that absorbs the rotational components of the crankshafts 7A, 7B, and 7C, and is used to transmit only the rotational components (revolutionary components) of the crankshafts 7A, 7B, and 7C, excluding their rotational components, to the planetary gear 3. The multiple rolling elements 51 are arranged between the outer peripheral surface of the eccentric portion 72 of each crankshaft 7A, 7B, and 7C and the inner peripheral surface of each opening 33 of the planetary gear 3. That is, the eccentric portion 72 of each crankshaft 7A, 7B, and 7C functions as the inner ring of the eccentric bearing 5, and the inner peripheral surface of each opening 33 of the planetary gear 3 functions as the outer ring of the eccentric bearing 5.

[0084] With the planetary gear 3 assembled with the eccentric bearing 5 and multiple crankshafts 7A, 7B, and 7C, when each crankshaft 7A, 7B, and 7C rotates (self-rotates), each eccentric part 72 rotates (eccentrically moves) around the axis Ax2. The planetary gear 3 is positioned in a direction parallel to the rotation axis Ax1 (axial direction) corresponding to each eccentric part 72. Therefore, the eccentric motion of each eccentric part 72 is transmitted to the planetary gear 3 via the eccentric bearing 5, and the planetary gear 3 oscillates around the rotation axis Ax1. In other words, the eccentric motion of the eccentric parts 72 in crankshafts 7A, 7B, and 7C is transmitted to the planetary gear 3. The eccentric bearing 5 serves to mitigate friction and other actions caused by the relative rotation based on the speed difference between the eccentric motion of the eccentric parts 72 of each crankshaft 7A, 7B, and 7C (that is, the self-rotation of each crankshaft 7A, 7B, and 7C) and the revolution of the planetary gear 3, and also serves to transmit power.

[0085] In the gear assembly 1 described above, a rotational force is applied to the input shaft 500 as input, causing the input shaft 500 to rotate around the rotation axis Ax1. This causes the planetary gear 3 to oscillate (revolve) around the rotation axis Ax1. At this time, the planetary gear 3 oscillates in a state where it is internally tangent to the internal gear 2 and a portion of its external teeth 31 meshes with a portion of the internal teeth 21. Therefore, as the input shaft 500 rotates, the meshing position of the internal teeth 21 and external teeth 31 moves along the circumference of the internal gear 2. This generates a relative rotation between the two gears (internal gear 2 and planetary gear 3) corresponding to the difference in the number of teeth between the planetary gear 3 and the internal gear 2. Furthermore, the rotational component (rotational component) of the planetary gear 3, excluding the oscillation component (revolutionary component), is transmitted to a pair of supports 18 and 19 via multiple crankshafts 7A, 7B, and 7C. As a result, a rotational output that is reduced in speed at a relatively high reduction ratio is obtained from a pair of supports 18 and 19, corresponding to the difference in the number of teeth of the two gears.

[0086] However, as described above, in the gear device 1 of this basic structure, the difference in the number of teeth between the internal gear 2 and the planetary gear 3 defines the reduction ratio of the output rotation relative to the input rotation in the gear device 1. That is, when the number of teeth of the internal gear 2 is set to "V1" and the number of teeth of the planetary gear 3 is set to "V2", the reduction ratio R1 is expressed by the following equation 1: R1=V2 / (V1-V2) (Equation 1)

[0087] In general, the smaller the difference in the number of teeth (V1-V2) between the internal gear 2 and the planetary gear 3, the larger the reduction ratio R1. As an example, the number of teeth V1 of the internal gear 2 is "72", the number of teeth V2 of the planetary gear 3 is "70", and the difference in the number of teeth (V1-V2) is "2". Therefore, according to Equation 1 above, the reduction ratio R1 is "35". In this case, viewed from the input side of the rotating shaft Ax1, when each crankshaft 7A, 7B, 7C rotates clockwise one revolution (360 degrees) around the axis Ax2 of the shaft center 71 (refer to Figures 5 and 6), the pair of supports 18, 19 rotate counterclockwise around the rotating shaft Ax1 by the amount of the difference in the number of teeth "2" (that is, about 10.3 degrees).

[0088] According to the gear assembly 1 of this basic structure, such a high reduction ratio R1 can be achieved through the combination of the internal gear 2 and the planetary gear 3. Furthermore, between the input gear 501 and the multiple crankshaft gears 502A, 502B, and 502C, an appropriate reduction ratio can also be achieved based on the number of teeth of the input gear 501 and the crankshaft gears 502A, 502B, and 502C. As a result, a high reduction ratio can be achieved as a whole as the gear assembly 1.

[0089] Alternatively, the gear assembly 1 may include at least an internal gear 2, planetary gears 3, crankshafts 7A, 7B, 7C, and a pair of supports 18, 19. For example, as shown in FIG4, it may also include a spacer 11. The spacer 11 is arranged in a direction (axial direction) parallel to the rotation axis Ax1 between a pair of planetary gears 3 (first planetary gear 301 and second planetary gear 302).

[0090] (Implementation Method 1)

[0091] As shown in Figures 7 to 9, the internal meshing planetary gear device 1A (hereinafter also simply referred to as "gear device 1A") of this embodiment differs from the basic structure gear device 1 mainly in the structure of the planetary gears 3 (first planetary gear 301 and second planetary gear 302). Hereinafter, for structures that are the same as those in the basic structure, the same reference numerals will be used and descriptions will be omitted as appropriate.

[0092] In this embodiment, as an example of gear device 1A, an internally oriented planetary gear device with cycloidal tooth profile is illustrated. That is, the gear device 1A of this embodiment includes an internally oriented planetary gear 3 with a cycloidal curved tooth profile. Here, the gear device 1A includes two planetary gears 3, a first planetary gear 301 and a second planetary gear 302, identical to the basic structure. The two planetary gears 3 are arranged around the rotation axis Ax1 with a phase difference of 180 degrees along a direction parallel to the rotation axis Ax1 (axial direction). The shapes of the first planetary gear 301 and the second planetary gear 302 are common, therefore, the structure of the planetary gear 3 will be described below using the first planetary gear 301 as an example.

[0093] In the gear device 1A of this embodiment, the following conditions are satisfied regarding the number of teeth of the external teeth 31 of the planetary gear 3 and the number of teeth of the internal teeth 21 of the internal gear 2. That is, in this embodiment, the number of teeth of the internal teeth 21 and the number of teeth of the external teeth 31 are both odd, and the difference between the number of teeth of the internal teeth 21 and the external teeth 31 is "2".

[0094] Specifically, the tooth profile of the external tooth 31 of the planetary gear 3 is represented, for example, by a subcycloid TC1 as shown in Figure 7. The subcycloid TC1 illustrated in Figure 7 is a trajectory drawn by setting the ratio of the diameter of the base circle to the diameter of the rotating circle to a non-integer (for example, "13 / 2"), and by setting the point within the rotating circle that returns to the starting point after the rotating circle rolls twice around the outer circumference of the base circle and rotates without slipping on the outer circumference of the base circle.

[0095] Furthermore, as shown in Figure 8, the innermost curved portion (the thicker line portion in Figure 8) of the double-drawn subcycloid TC1 is used as the tooth profile curve of the outer tooth 31 of the planetary gear 3. This achieves a planetary gear 3 with an odd number of teeth ("13" in the example of Figure 8). The number of teeth in the outer tooth 31, formed by the subcycloid TC1 which is set to return to the starting point after rolling two revolutions around the outer circumference of the base circle, is necessarily odd. In Figure 8, the portion of the outer tooth 31 formed on the outer periphery of the planetary gear 3 is shown by a diagonal line.

[0096] As shown in Figure 9, the planetary gear 3 with external teeth 31 having the tooth profile described above meshes with the internal teeth 21 of the internal gear 2. Here, the number of pins 23 constituting the internal teeth 21 is set to be two more than the number of teeth of the external teeth 31. That is, the number of teeth of the internal teeth 21 of the internal gear 2 is "15", which is "2" more than the number of teeth of the external teeth 31 of the planetary gear 3 ("13" in this case). Thus, not only the number of teeth of the external teeth 31, but also the number of teeth of the internal teeth 21 is an odd number ("15" in the example of Figure 9). Furthermore, the difference in the number of teeth between the internal teeth 21 and the external teeth 31 is "2".

[0097] In this embodiment, the tooth profile curve of the outer tooth 31 of the planetary gear 3 is located on the subcycloid TC1, and the planetary gear 3 oscillates (rotates eccentrically) inside the inner gear 2, which is composed of an arc tooth profile with two more teeth than its outer tooth 31. Thus, as shown in FIG9, at least a portion of the outer tooth 31 and the inner tooth 21 are opposite each other with a gap. Since the difference in the number of teeth between the outer tooth 31 and the inner tooth 21 is "2", they will not mesh with each other in the circumferential direction.

[0098] Thus, the planetary gear 3 oscillates (revolves) around the rotation axis Ax1 inside the internal gear 2, causing the external teeth 31 to partially mesh with the internal teeth 21. In other words, by oscillating around the rotation axis Ax1, a portion of the teeth constituting the external teeth 31 meshes with a portion of the teeth constituting the internal teeth 21. As a result, in the gear assembly 1A, a portion of the external teeth 31 can mesh with a portion of the internal teeth 21.

[0099] In Figures 7-9, a specific example is shown where both the number of teeth on the internal tooth 21 and the number of teeth on the external tooth 31 are odd, and the difference between the number of teeth on the internal tooth 21 and the external tooth 31 is "2". The example shown has "13" teeth on the external tooth 31 and "15" teeth on the internal tooth 21. However, the number of teeth on the internal tooth 21 and the external tooth 31 is not limited to this example. For example, in the case of a subcycloid generated by setting the ratio of the diameter of the base circle to the diameter of the turning circle to "23 / 2" and the turning circle returning to the starting point after rolling two revolutions around the outer circumference of the base circle, the number of teeth on the external tooth 31 is "23" and the number of teeth on the internal tooth 21 is "25".

[0100] Next, referring to FIGS. 10 and 11, the gear device 1X of the comparative example (referring to FIG. 11) will be described. In the gear device 1X of the comparative example, instead of the conditions of this embodiment, the number of teeth of the external teeth 31 of the planetary gear 3 and the number of teeth of the internal teeth 21 of the internal gear 2 are both even numbers, and the difference between the number of teeth of the internal teeth 21 and the external teeth 31 is "2".

[0101] Specifically, in the comparative example, the tooth profile of the external tooth 31 of the planetary gear 3 is represented, for example, by two subcycloids TC11 and TC12 as shown in Figure 10. Each subcycloid TC11 and TC12 illustrated in Figure 10 is a trajectory drawn by a point set within the rotating circle that returns to the starting point after the rotating circle rolls one revolution around the outer circumference of the base circle, with the diameter ratio of the base circle to the rotating circle set to an integer (for example, "11").

[0102] Furthermore, as shown in Figure 11, with the two subcycloids TC11 and TC12 staggered in phase overlap, the innermost curved portion (the thicker line portion in Figure 11) is used as the tooth profile curve of the external tooth 31 of the planetary gear 3. In the examples of Figures 10 and 11, each subcycloid TC11 and TC12 has 11 hills, which is the ratio of the base circle to the turning circle diameter. These two subcycloids TC11 and TC12 are staggered in phase overlap by 180 degrees or one hill spacing in the manner of overlapping hills and valleys.

[0103] Thus, the planetary gear 3 achieves an even number of teeth on the external gear 31 (20 in the example of Figure 11). The number of teeth on the external gear 31, formed by the superposition of two subcycloids TC11 and TC12, which are set in such a way that they return to the starting point after rolling one revolution around the outer circumference of the base circle, must be even. In Figure 11, the portion of the external gear 31 formed on the outer circumference of the planetary gear 3 is shown by the diagonal lines.

[0104] In the internal gear 2 combined with the planetary gear 3 having the aforementioned tooth profile of the external teeth 31, the number of pins 23 constituting the internal teeth 21 is set to be two more than the number of teeth of the external teeth 31. That is, the number of teeth of the internal teeth 21 of the internal gear 2 is "22", which is "2" more than the number of teeth of the external teeth 31 of the planetary gear 3 ("20" here). Thus, not only the number of teeth of the external teeth 31, but also the number of teeth of the internal teeth 21 is an even number.

[0105] As with the gear assembly 1X in the comparative example described above, in a structure where both the number of teeth on the internal gear 21 and the number of teeth on the external gear 31 are even, since the external gear 31 is formed by the superposition of two subcycloids TC11 and TC12, it does not share a pair of adjacent teeth on the external gear 31 with the teeth of the meshing internal gear 21. Therefore, when the input shaft 500 rotates around the rotation shaft Ax1 with a reduction ratio (e.g., "11"), the same teeth mesh between the external gear 31 and the internal gear 21 occurs every time the planetary gear 3 rotates once. As a result, in the gear assembly 1X of the comparative example, when damage (surface-starting point type peeling) occurs between the external gear 31 and the internal gear 21, for example, starting from an indentation caused by the meshing of foreign matter such as abrasive powder, a combination of meshing related to the growth of the surface-starting point occurs every time the planetary gear 3 rotates once, which may cause the damage to progress more rapidly.

[0106] In this case, as with the gear device 1A of this embodiment, in a structure where both the number of teeth on the internal gear 21 and the number of teeth on the external gear 31 are odd, since the external gear 31 is formed by a subcycloid TC1 that is already offset, there is a pair of adjacent teeth on the external gear 31 and the teeth on the meshing internal gear 21. Therefore, when the input shaft 500 rotates around the rotation shaft Ax1 at a reduction ratio (e.g., "11.5") twice (e.g., "23"), after the planetary gear 3 has rotated twice, the same teeth mesh between the external gear 31 and the internal gear 21. As a result, in the gear device 1A of this embodiment, when damage occurs between the external gear 31 and the internal gear 21, for example, starting from an indentation caused by the meshing of foreign matter such as wear powder, the planetary gear 3 does not produce a combination of meshing related to the growth of the surface starting point before it has rotated twice. As a result, compared with the comparative example above, the progression of damage is delayed by 1 / 2, and thus the lifespan of the gear device 1A can be extended by approximately twice.

[0107] As described above, the gear device 1A of this embodiment includes: an internal gear 2 having internal teeth 21; a planetary gear 3 having external teeth 31 that partially mesh with the internal teeth 21; and a plurality of eccentric shafts (crankshafts 7A, 7B, 7C). The plurality of eccentric shafts are positioned offset from the rotation axis Ax1, which serves as the axis of the internal gear 2, and are synchronously driven by the input gear 501. The gear device 1A is an internal meshing planetary gear device that causes the planetary gear 3 to oscillate by the plurality of eccentric shafts, thereby causing the planetary gear 3 to rotate relative to the internal gear 2 about the rotation axis Ax1. Here, the number of teeth of both the internal teeth 21 and the external teeth 31 is odd, and the difference between the number of teeth of the internal teeth 21 and the external teeth 31 is 2.

[0108] According to this structure, even if damage occurs between the external teeth 31 and the internal teeth 21, for example, starting from an indentation caused by the meshing of a foreign object, the progression of the damage can be slowed down, thus providing a gear device 1A that is less prone to reliability degradation. Furthermore, the gear device 1A of this embodiment is particularly less prone to reliability degradation during long-term use, thus also resulting in improved transmission efficiency, longer service life, and higher performance of the gear device 1A.

[0109] In this embodiment, the gear assembly 1A includes a first planetary gear 301 and a second planetary gear 302. That is, in addition to the first planetary gear 301 serving as a planetary gear 3, the gear assembly 1A also includes a second planetary gear 302 having a second external tooth that partially meshes with the internal tooth 21. The planetary gear 3 has a first external tooth that serves as an external tooth 31. Eccentric shafts (crankshafts 7A, 7B, 7C) respectively cause the first planetary gear 301 and the second planetary gear 302 to oscillate and rotate.

[0110] In this way, by including multiple planetary gears 3 (first planetary gear 301 and second planetary gear 302), the gear device 1A can achieve a balance of weight and load among the multiple planetary gears 3. Furthermore, with respect to each planetary gear 3 (first planetary gear 301 and second planetary gear 302), the progression of damage starting from the indentation between the external teeth 31 and the internal teeth 21 can be slowed down.

[0111] Furthermore, the number of teeth on the second external tooth is the same as the number of teeth on the first external tooth. That is, the number of teeth on the first external tooth (external tooth 31) of the first planetary gear 301 is the same as the number of teeth on the second external tooth (external tooth 31) of the second planetary gear 302.

[0112] Therefore, in either the first planetary gear 301 or the second planetary gear 302, the same conditions can be satisfied regarding the relationship with the internal gear 2 (the number of teeth of the internal gear 21 and the number of teeth of the external gear 31 are both odd, and the difference between the number of teeth of the internal gear 21 and the external gear 31 is "2"). As a result, in either the first planetary gear 301 or the second planetary gear 302, the progression of damage starting from the indentation between the external gear 31 and the internal gear 21 can be slowed down.

[0113] Furthermore, in the gear device 1A of this embodiment, the internal gear 2 has an annular gear body 22 and a plurality of pins 23 constituting the internal teeth 21. The plurality of pins 23 are held in a rotatable state in a plurality of inner circumferential grooves 223 formed on the inner circumferential surface 221 of the gear body 22.

[0114] Thus, for example, by creating irregularities on the surfaces of the plurality of pins 23 constituting the internal tooth 21, even if damage originating from an indentation occurs between the external tooth 31 and the internal tooth 21, the progression of the damage can be slowed.

[0115] However, as shown in FIG12, the gear device 1A of this embodiment, together with the first component 201 and the second component 202, constitutes a robot joint device 200 (i.e., a robot arm structure). In other words, the robot joint device 200 equipped with the robot arm structure of this embodiment includes the gear device 1A, the first component 201, and the second component 202. The first component 201 is fixed to the internal gear 2. The second component 202 rotates relative to the first component 201 as the planetary gear 3 rotates relative to the internal gear 2. FIG12 is a schematic cross-sectional view of the robot joint device 200. In addition, the first component 201, the second component 202, and the drive source 101 are schematically shown in FIG12.

[0116] The robot joint device 200 configured in this way functions as a joint device by rotating the first member 201 and the second member 202 relative to each other about the rotation axis Ax1. Here, the first member 201 and the second member 202 rotate relative to each other by driving the input shaft 500 of the gear device 1A by the drive source 101. At this time, the rotation generated by the drive source 101 (input rotation) is reduced in the gear device 1A with a relatively high reduction ratio, and the first member 201 or the second member 202 is driven with a relatively high torque. That is to say, the first member 201 and the second member 202 connected by the gear device 1A can perform flexion and extension movements about the rotation axis Ax1.

[0117] The robot joint device 200 (i.e., the robot arm structure) is used, for example, in robots such as horizontal articulated robots (jointed robots). Furthermore, the robot joint device 200 is not limited to horizontal articulated robots; for example, it can also be used in industrial robots other than horizontal articulated robots, or robots other than industrial robots. Additionally, the gear device 1A of this embodiment is not limited to the robot joint device 200; for example, as a wheel device such as a hub motor, it can also be used in vehicles such as Automated Guided Vehicles (AGVs).

[0118] <Variation Example>

[0119] Embodiment 1 is merely one of the various embodiments of the present invention. Various modifications can be made to Embodiment 1 based on design, etc., as long as the objective of the present invention is achieved. Furthermore, the accompanying drawings referenced in this invention are schematic diagrams, and the ratios of the size and thickness of each structural element in the drawings are not necessarily limited to reflecting actual dimensional ratios. Below, variations of Embodiment 1 are listed. The variations described below can be appropriately combined and applied.

[0120] The number of crankshafts 7A, 7B, and 7C is not limited to "3" and can also be 2 or 4 or more. Furthermore, if there is only one crankshaft, it is not a distribution type, but an eccentric oscillating type internal meshing planetary gear device that achieves alignment between the rotation axis Ax1 and the crankshaft axis Ax2. In this case, by driving the crankshaft, the planetary gear 3 oscillates, and a pair of supports 18 and 19 can rotate relative to the gear body 22 about the rotation axis Ax1.

[0121] Furthermore, in Embodiment 1, a gear device 1A with two planetary gears 3 is illustrated; however, gear device 1A may also include three or more planetary gears 3. For example, when gear device 1A includes three planetary gears 3, it is preferable that these three planetary gears 3 are arranged with a phase difference of 120 degrees around the rotation axis Ax1. Alternatively, gear device 1A may include only one planetary gear 3. Or, when gear device 1A includes three planetary gears 3, two of these three planetary gears 3 may be in the same phase, and the remaining planetary gear 3 may be arranged with a phase difference of 180 degrees around the rotation axis Ax1.

[0122] In addition, bearing component 6 can be a crossed roller bearing, a deep groove ball bearing, or a four-point contact ball bearing, etc.

[0123] Furthermore, the number of teeth of the input gear 501, the number of teeth of the crankshaft gears 502A, 502B, and 502C, the number of pins 23 (the number of teeth of the internal gear 21), and the number of teeth of the external gear 31 described in Embodiment 1 are merely examples and can be appropriately modified.

[0124] Furthermore, the eccentric bearing 5 is not limited to roller ball bearings; for example, it can also be a deep groove ball bearing or an angular contact ball bearing.

[0125] Furthermore, the materials of the various structural elements of the gear device 1A are not limited to metal; for example, they can be resins such as engineering plastics.

[0126] Furthermore, the gear device 1A is only required to output the relative rotation between the inner ring 61 and the outer ring 62 of the bearing member 6, and is not limited to outputting the rotational force of the inner ring 61 (input-side bracket 18 and output-side bracket 19). For example, the rotational force of the outer ring 62 (housing 10) that rotates relative to the inner ring 61 can also be output.

[0127] In addition, lubricants are not limited to liquid substances such as lubricating oil (oil), but can also be gel-like substances such as lubricating grease.

[0128] (Summarize)

[0129] As described above, the first-form internal meshing planetary gear device (1, 1A) includes: an internal gear (2) having internal teeth (21); a planetary gear (3) having external teeth (31) that partially mesh with the internal teeth (21); and multiple eccentric shafts (crankshafts 7A, 7B, 7C). The multiple eccentric shafts are positioned offset from the rotation axis (Ax1) which is the axis of the internal gear (2) and are synchronously driven by the input gear (501). The internal meshing planetary gear device (1, 1A) is an internal meshing planetary gear device that rotates relative to the internal gear (2) about the rotation axis (Ax1) by oscillating the planetary gear (3) with the multiple eccentric shafts. The number of teeth of the internal teeth (21) and the number of teeth of the external teeth (31) are both odd, and the difference between the number of teeth of the internal teeth (21) and the external teeth (31) is 2.

[0130] According to this configuration, even if damage occurs between the external teeth (31) and the internal teeth (21) starting from an indentation caused by the meshing of a foreign object, the progression of the damage can be slowed down, thus providing an internal meshing planetary gear device (1, 1A) that is less prone to reliability degradation. Therefore, an internal meshing planetary gear device (1, 1A) is realized where damage starting from an indentation between the external teeth (31) and the internal teeth (21) is difficult to progress.

[0131] In the second form of the internal meshing planetary gear device (1, 1A), based on the first form, in addition to the first planetary gear (301) which is a planetary gear (3) having a first external tooth as an external tooth (31), a second planetary gear (302) having a second external tooth that partially meshes with the internal tooth (21) is also included. Eccentric shafts (crankshafts 7A, 7B, 7C) cause the first planetary gear (301) and the second planetary gear (302) to oscillate and rotate, respectively.

[0132] According to this configuration, the internal meshing planetary gear assembly (1, 1A) can achieve a balance of weight and load among the multiple planetary gears (3). Furthermore, regarding each of the first planetary gears (301) and the second planetary gears (302), the progression of damage originating from the indentation between the external teeth (31) and the internal teeth (21) can be slowed down.

[0133] In the third form of the internal meshing planetary gear device (1, 1A), based on the second form, the number of teeth of the second external tooth is the same as the number of teeth of the first external tooth.

[0134] According to this configuration, in either the first planetary gear (301) or the second planetary gear (302), the same conditions can be satisfied regarding their relationship with the internal gear (2) (the number of teeth of both the internal gear (21) and the external gear (31) are odd, and the difference between the number of teeth of the internal gear (21) and the external gear (31) is "2"). As a result, in either the first planetary gear (301) or the second planetary gear (302), the progression of damage originating from the indentation between the external gear (31) and the internal gear (21) can be slowed down.

[0135] In the fourth form of the internal meshing planetary gear device (1, 1A), based on any of the first to third forms, the internal gear (2) has an annular gear body (22) and multiple pins (23) constituting the internal teeth (21). The multiple pins (23) are held in a rotatable state in multiple inner circumferential grooves (223) formed on the inner circumferential surface (221) of the gear body (22).

[0136] According to this morphology, for example, by creating irregularities on the surfaces of the multiple pins (23) constituting the inner tooth (21), even if damage originating from an indentation occurs between the outer tooth (31) and the inner tooth (21), the progression of the damage can be slowed.

[0137] The fifth type of robot joint device (200) includes: an internal meshing planetary gear device (1, 1A) of any of the first to fourth types; a first member (201) fixed to the internal gear (2); and a second member (202) that rotates relative to the first member (201) as the planetary gear (3) rotates relative to the internal gear (2).

[0138] According to this configuration, a robotic joint device (200) can be realized that damage is not easily advanced from the indentation generated between the outer tooth (31) and the inner tooth (21).

[0139] Regarding the structures of the second to fourth forms, these are not essential for the internal meshing planetary gear devices (1, 1A) and can be omitted appropriately.

[0140] Explanation of reference numerals in the attached figures: 1. 1A Internal meshing planetary gear assembly; 2. Internal gear; 3. Planetary gear; 7A, 7B, 7C Crankshaft (eccentric shaft); 21 Internal gear; 22 Gear body; 23 Pin; 31 External gear (first external gear, second external gear); 200 Robot joint device (i.e., robot arm structure); 201 First component; 202 Second component; 221 Inner circumferential surface; 223 Inner circumferential groove; 301 First planetary gear; 302 Second planetary gear; 501 Input gear; Ax1 Rotating shaft. Industrial applicability

[0141] According to embodiments of the present invention, a robotic arm structure including a robotic joint device and an internal meshing planetary gear device can be provided, which makes it difficult for damage to progress from an indentation generated between the external and internal teeth. The robotic joint device includes the internal meshing planetary gear device.

Claims

1. A robotic arm structure, comprising a joint device for the robot, wherein, The robot joint device includes: An internal meshing planetary gear device includes: an internal gear having internal teeth; a planetary gear having external teeth that partially mesh with the internal teeth; and a plurality of eccentric shafts disposed at positions offset from a rotation axis that serves as the axis of the internal gear, synchronously driven by an input gear, wherein the planetary gear is oscillated by the plurality of eccentric shafts, thereby causing the planetary gear to rotate relative to the internal gear about the rotation axis, wherein the number of teeth of the internal gear and the number of teeth of the external gear are both odd, and the difference between the number of teeth of the internal gear and the number of teeth of the external gear is 2; The first component is fixed to the internal gear; and The second component rotates relative to the first component as the planetary gear rotates relative to the internal gear.

2. An internal meshing planetary gear device, comprising: Internal gear, having internal teeth; A planetary gear having external teeth that partially mesh with the internal teeth; and Multiple eccentric shafts, positioned offset from the rotational axis that serves as the axis of the internal gear, are synchronously driven by an input gear. By oscillating the planetary gears using the plurality of eccentric shafts, the planetary gears rotate relative to the internal gears about the axis of rotation. in, Both the number of teeth on the inner teeth and the number of teeth on the outer teeth are odd numbers. The difference in the number of teeth between the internal teeth and the external teeth is 2.

3. The internal meshing planetary gear device according to claim 2, wherein, In addition to the first planetary gear having a first external tooth that serves as the external tooth, the internal meshing planetary gear assembly also has a second planetary gear having a second external tooth that partially meshes with the internal tooth. The eccentric shaft causes the first planetary gear and the second planetary gear to oscillate and rotate, respectively.

4. The internal meshing planetary gear device according to claim 3, wherein, The number of teeth on the second external tooth is the same as the number of teeth on the first external tooth.

5. The internal meshing planetary gear device according to any one of claims 2 to 4, wherein, The internal gear has: an annular gear body; and a plurality of pins, which are held in a rotatable state in a plurality of inner circumferential grooves formed on the inner circumferential surface of the gear body, and constitute the internal teeth.

6. A joint device for a robot, wherein, include: The internal meshing planetary gear device according to any one of claims 2 to 5; The first component is fixed to the internal gear; and The second component rotates relative to the first component as the planetary gear rotates relative to the internal gear.

Images