Robot mechanical arm structure, internal meshing planetary gear system, and robot joint system

Abstract

The present invention provides a robotic mechanical arm structure equipped with a robotic joint device that is less susceptible to damage progression originating from indentations between external and internal teeth, and an internal meshing planetary gear device. [Solution] The internally meshing planetary gear device comprises 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 the axis of rotation, which is the axis of the internal gear, and are driven synchronously by an input gear. The internally meshing planetary gear device rotates the planetary gear relative to the internal gear around the axis of rotation by oscillating the planetary gear with the plurality of eccentric shafts. The number of teeth of both the internal and external teeth is odd, and the difference in the number of teeth between the internal and external teeth is 2. This makes it difficult for damage to progress starting from indentations formed between the external and internal teeth.

Description

Technical Field

[0005] ,

[0001] The present disclosure relates to the field of robotics, and particularly to a robotic arm structure equipped with a robotic joint device and an internal meshing planetary gear device. The robotic joint device includes the internal meshing planetary gear device.

Background Art

[0002] As a related technique, an internal meshing planetary gear device (speed reducer) using a trochoid gear as a planetary gear is known. In this internal meshing planetary gear device, a planetary gear (external gear) held by an eccentric wheel rotates eccentrically within an internal gear (internal gear) having a fixed arc tooth profile, and the planetary gear is rotated in the opposite direction as the eccentric wheel rotates.

[0003] In the internal meshing planetary gear device according to the related technique, the radius ratio of the rolling circle to the base circle is not an integer, and a trochoid gear using the innermost overlapping portion of the trochoid curve where the rolling circle rotates multiple times around the base circle and returns to the starting point as the tooth profile curve is used as the planetary gear. In this case, both the number of teeth of the internal teeth of the internal gear and the number of teeth of the external teeth of the planetary gear are odd numbers, and the tooth number difference is "2".

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The configuration of the above-mentioned related technologies is not of the distribution type. In eccentric oscillating internal meshing planetary gear systems, which are referred to as distribution type, the number of teeth on the internal gear and the number of teeth on the external gear are both odd, and there are no configurations that employ a difference of "2" between the number of teeth. Therefore, in distribution type internal meshing planetary gear systems, if damage (surface-initiated flaking) occurs between the external and internal teeth, starting from an indentation caused by foreign matter such as wear particles, a combination of meshing occurs that leads to the growth of surface-initiated flaking each time the planetary gear rotates, and damage may progress relatively quickly.

[0006] The purpose of this disclosure is to provide a robotic mechanical arm structure and an internal meshing planetary gear system, which includes a robotic joint device having an internal meshing planetary gear system that is less susceptible to damage progression starting from indentations between external and internal teeth. [Means for solving the problem]

[0007] A robotic mechanical arm structure according to one aspect of the present disclosure includes a robotic joint device. The robotic joint device includes an internal meshing planetary gear device, a first member, and a second member. The 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. The plurality of eccentric shafts are positioned offset from the axis of rotation, which is the axis of the internal gear, and are driven synchronously by an input gear. The internal meshing planetary gear device rotates the planetary gear relative to the internal gear around the axis of rotation by oscillating the planetary gear with the plurality of eccentric shafts. The number of teeth of the internal teeth and the number of teeth of the external teeth are both odd, and the difference in the number of teeth between the internal teeth and the external teeth is 2. The first member is fixed to the internal gear. The second member rotates relative to the first member in accordance with the relative rotation of the planetary gear with respect to the internal gear.

[0008] An internally meshing planetary gear device according to one aspect of the present disclosure comprises 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 the axis of rotation, which is the axis of the internal gear, and are driven synchronously by an input gear. The internally meshing planetary gear device rotates the planetary gear relative to the internal gear around the axis of rotation by oscillating the planetary gear with the plurality of eccentric shafts. The number of teeth of the internal teeth and the number of teeth of the external teeth are both odd, and the difference in the number of teeth between the internal teeth and the external teeth is 2.

[0009] A robotic joint device according to one aspect of the present disclosure comprises an internal meshing planetary gear device, a first member fixed to the internal gear, and a second member that rotates relative to the first member in accordance with the relative rotation of the planetary gear with respect to the internal gear. [Effects of the Invention]

[0010] According to this disclosure, it is possible to provide a robotic mechanical arm structure and an internal meshing planetary gear device, which is equipped with a robotic joint device having an internal meshing planetary gear device that is less susceptible to damage progression starting from indentations between external and internal teeth. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a perspective view showing the schematic configuration of an actuator, including an internally meshing planetary gear system, which is part of the basic configuration. [Figure 2] Figure 2 is a schematic exploded perspective view of the same internally meshed planetary gear system as seen from the input side of the rotating shaft. [Figure 3] Figure 3 is a schematic exploded perspective view of the same internally meshing planetary gear mechanism as seen from the output side of the rotating shaft. [Figure 4] Figure 4 is a schematic cross-sectional view of the internally meshing planetary gear set shown above. [Figure 5] Figure 5 is a cross-sectional view taken along line A1-A1 in Figure 4, showing the same internally meshed planetary gear mechanism. [Figure 6]Figure 6 is a cross-sectional view taken along line B1-B1 in Figure 4, showing the same internally meshing planetary gear system. [Figure 7] Figure 7 is a schematic diagram showing an example of a trochoid curve that constitutes the tooth profile curve of the external teeth of a planetary gear in an internally meshing planetary gear system according to Embodiment 1. [Figure 8] Figure 8 is a schematic diagram showing an example of a planetary gear in the internal meshing planetary gear system described above. [Figure 9] Figure 9 is a schematic diagram showing an example of the planetary gear and internal gear 2 of the internal meshing planetary gear system described above. [Figure 10] Figure 10 is a schematic diagram showing an example of a trochoid curve that constitutes the tooth profile curve of the external teeth of a planetary gear in an internally meshing planetary gear system according to a comparative example. [Figure 11] Figure 11 is a schematic diagram showing an example of a planetary gear in the internal meshing planetary gear system described above. [Figure 12] Figure 12 is a schematic diagram showing a robot joint device using the internal meshing planetary gear system described above. [Modes for carrying out the invention]

[0012] (Basic configuration) (1) Overview The following describes the outline of the internally meshing planetary gear unit 1 relating to this basic configuration with reference to Figures 1 to 4. The drawings referenced in this disclosure are all schematic, and the ratios of the size and thickness of each component shown in the figures do not necessarily reflect the actual dimensional ratios. For example, the tooth profile, dimensions, and number of teeth of the internal teeth 21 and external teeth 31 in Figures 1 to 4 are all shown schematically for illustrative purposes only and are not intended to limit the actual shape to those shown.

[0013] The internal meshing planetary gear device 1 according to this basic configuration (hereinafter, also simply referred to as "gear device 1") is a gear device including an internal gear 2 and a planetary gear 3. In this gear device 1, the planetary gear 3 is disposed inside the annular internal gear 2, and by swinging the planetary gear 3, the planetary gear 3 is rotated relative to the internal gear 2. Further, the internal meshing planetary gear device 1 further includes a bearing member 6 having an outer ring 62 and an inner ring 61. The inner ring 61 is disposed inside the outer ring 62 and is supported so as to be rotatable relative to the outer ring 62. In particular, the gear device 1 according to this basic configuration is an eccentric swing type internal meshing planetary gear device called a distribution type.

[0014] As shown in FIGS. 1 to 4, the gear device 1 according to this basic configuration includes a plurality (three in the basic configuration) of crank shafts (eccentric shafts) 7A, 7B, 7C disposed at positions offset from the axis (rotation axis Ax1) of the internal gear 2. Further, the gear device 1 includes an input shaft 500 centered on the rotation axis Ax1 and disposed on the axis (rotation axis Ax1) of the internal gear 2, and an input gear 501 integrally formed with the input shaft 500. Crank shaft gears 502A, 502B, 502C are spline-connected to the plurality of crank shafts 7A, 7B, 7C, respectively. These plurality (three in the basic configuration) of crank shaft gears 502A, 502B, 502C are arranged so as to mesh with the input gear 501. Therefore, when the input shaft 500 is driven, the gear device 1 swings the planetary gear 3 by synchronously driving the crank shafts 7A, 7B, 7C by the input gear 501.

[0015] The internal gear 2 has internal teeth 21 and is fixed to the outer ring 62. In particular, in this basic configuration, the internal gear 2 has an annular gear body 22 and a plurality of outer pins 23. The plurality of outer pins 23 are held on the inner peripheral surface 221 of the gear body 22 in a rotatable state and constitute 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 inscribed with respect to the internal gear 2, and a part of the external teeth 31 meshes with a part of the internal teeth 21. In this state, when the plurality of crankshafts 7A, 7B, 7C are driven, the planetary gear 3 swings, and the meshing position between the internal teeth 21 and the external teeth 31 moves in the circumferential direction of the internal gear 2, and a relative rotation corresponding to the difference in the number of teeth between the planetary gear 3 and the internal gear 2 occurs between the two gears (the internal gear 2 and the planetary gear 3). Here, if the internal gear 2 is fixed, the planetary gear 3 rotates (self-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 planetary gear 3 according to the difference in the number of teeth between the two gears.

[0016] This type of gear device 1 is used to extract the rotation corresponding to the self-rotation component of the planetary gear 3 as the rotation of a pair of carriers 18, 19 that are relatively fixed by means such as integration or fitting with the inner ring 61 of the bearing member 6. Thereby, the gear device 1 functions as a gear device with a relatively high reduction ratio, with the input shaft 500 as the input side and the pair of carriers 18, 19 as the output side. Therefore, in the gear device 1 according to this basic configuration, in order to transmit the rotation corresponding to the self-rotation component of the planetary gear 3 to the pair of carriers 18, 19, the pair of carriers 18, 19 support the plurality of crankshafts 7A, 7B, 7C. The pair of carriers 18, 19 are arranged on both sides in the axial direction of the planetary gear 3 (the direction along the rotation axis Ax1) and rotatably support each crankshaft 7A, 7B, 7C.

[0017] Here, the multiple crankshafts 7A, 7B, and 7C are inserted into multiple openings 33 formed in the planetary gear 3, and rotate relative to the internal gear 2 as the planetary gear 3 rotates. Each crankshaft 7A, 7B, and 7C has an axial portion 71 and an eccentric portion 72 that is eccentric to the axial portion 71. A pair of carriers 18 and 19 rotatably support the axial portion 71 of each crankshaft 7A, 7B, and 7C, and the eccentric portions 72 of each crankshaft 7A, 7B, and 7C are inserted into the openings 33 of the planetary gear 3. As each crankshaft 7A, 7B, and 7C rotates around its respective axial portion 71, each eccentric portion 72 rotates eccentrically (eccentric motion) relative to its respective axial portion 71. Consequently, the planetary gear 3 oscillates. As the planetary gear 3 oscillates, it partially meshes with the internal gear 2 and rotates relative to the internal gear 2. As a result, the planetary gear 3 rotates on its own central axis while revolving within the internal gear 2 around the rotation axis Ax1. As the planetary gear 3 rotates, each crankshaft 7A, 7B, and 7C revolves around the rotation axis Ax1, and the carriers 18 and 19 that support the axial center 71 of each crankshaft 7A, 7B, and 7C rotate in accordance with the revolution of each crankshaft 7A, 7B, and 7C. In this way, the rotation (rotation component) of the planetary gear 3, excluding the oscillating component (revolution component), is transmitted to the pair of carriers 18 and 19 by multiple crankshafts 7A, 7B, and 7C.

[0018] Furthermore, the gear device 1 in this basic configuration, together with the drive source 101, constitutes an actuator 100, as shown in Figure 1. In other words, the actuator 100 in this basic configuration comprises the gear device 1 and the drive source 101. The drive source 101 generates a driving force to oscillate the planetary gear 3. Specifically, the drive source 101 oscillates the planetary gear 3 by rotating the input shaft 500 around the rotation axis Ax1.

[0019] (2) Definition As used in this disclosure, "ring-shaped" 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 (ring-shaped) that is a perfect circle in a plan view, but may also be an elliptical shape, a polygonal shape, etc. Furthermore, even a shape with a bottom, such as a cup shape, is included in "ring-shaped" if its peripheral wall is ring-shaped.

[0020] In this disclosure, "revolution" means that an object revolves 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 the orbital path centered on the axis of rotation. Therefore, for example, if an object rotates around an eccentric axis parallel to the central axis passing through its center (center of gravity), the object is revolving around the eccentric axis as its axis of rotation. As an example, the planetary gear 3 revolves inside the internal gear 2 by oscillating, so as to revolve around the axis of rotation Ax1.

[0021] Furthermore, in this disclosure, one side of the rotating shaft Ax1 (the left side in Figure 4) may be referred to as the "output side," and the other side of the rotating shaft Ax1 (the right side in Figure 4) may be referred to as the "input side." In the example in Figure 4, rotation is applied to the input shaft 500 from the "input side" of the rotating shaft Ax1, and the rotation of the pair of carriers 18 and 19 is extracted from the "output side" of the rotating shaft Ax1. However, "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 seen from the gear device 1.

[0022] In this disclosure, "axis of rotation" refers to a virtual axis (straight line) that is the center of the rotational motion of the rotating body. In other words, the axis of rotation Ax1 is a virtual axis that does not have a physical form. The input shaft 500 performs rotational motion around the axis of rotation Ax1.

[0023] 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 internal gear 2 consist of a collection of multiple teeth arranged on the inner circumferential surface 221 of the internal gear 2 (gear body 22). Similarly, the external teeth 31 of the planetary gear 3 consist of a collection of multiple teeth arranged on the outer circumferential surface of the planetary gear 3.

[0024] (3) Composition The detailed configuration of the internally meshing planetary gear unit 1 related to this basic configuration will be explained below with reference to Figures 1 to 6.

[0025] Figure 1 is a perspective view showing the schematic configuration of the actuator 100 including the gear unit 1. In Figure 1, the drive source 101 is schematically shown. Figure 2 is a schematic exploded perspective view of the gear unit 1 as seen from the input side of the rotating shaft Ax1. Figure 3 is a schematic exploded perspective view of the gear unit 1 as seen from the output side of the rotating shaft Ax1. Figure 4 is a schematic cross-sectional view of the gear unit 1. Figure 5 is a cross-sectional view taken along line A1-A1 in Figure 4. Figure 6 is a cross-sectional view taken along line B1-B1 in Figure 4. However, in Figures 5 and 6, hatching is omitted for parts other than the crankshafts 7A, 7B, and 7C, even in cross-sections.

[0026] (3.1) Overall structure As shown in Figures 1 to 4, the gear unit 1 in this basic configuration comprises an internal gear 2, a planetary gear 3, a bearing member 6, a plurality of crankshafts 7A, 7B, 7C, a pair of carriers 18, 19, and an input shaft 500. Furthermore, in this basic configuration, the gear unit 1 further comprises an input gear 501, a plurality of crankshaft gears 502A, 502B, 502C, a pair of rolling bearings 41, 42, an eccentric bearing 5, and a case 10. In this basic configuration, the materials of the components of the gear unit 1, such as the internal gear 2, planetary gear 3, the plurality of crankshafts 7A, 7B, 7C, and the pair of carriers 18, 19, are metals such as stainless steel, cast iron, carbon steel for machine structures, chromium-molybdenum steel, phosphor bronze, or aluminum bronze, or light metals such as aluminum or titanium. The term "metal" (including light metals) here includes metals that have undergone surface treatment such as nitriding.

[0027] Furthermore, in this basic configuration, an internal planetary gear system using a trochoidal tooth profile is given as an example of the gear system 1. In other words, the gear system 1 in this basic configuration is equipped with an internal planetary gear 3 having a trochoidal curved tooth profile.

[0028] Furthermore, in this basic configuration, as an example, the gear device 1 is used with the gear body 22 of the internal gear 2 fixed to a fixed member such as the case 10, together with the outer ring 62 of the bearing member 6. As a result, the planetary gear 3 rotates relative to the fixed member (case 10, etc.) as the internal gear 2 and the planetary gear 3 rotate relative to each other.

[0029] Furthermore, in this basic configuration, when the gear unit 1 is used as the actuator 100, a rotational force is applied to the input shaft 500 as input, and a rotational force is extracted as output from the pair of carriers 18 and 19 integrated with the inner ring 61 of the bearing member 6. In other words, the gear unit 1 operates with the rotation of the input shaft 500 as the input rotation and the rotation of the pair of carriers 18 and 19 integrated with the inner ring 61 as the output rotation. As a result, the gear unit 1 obtains an output rotation that is reduced with a relatively high reduction ratio relative to the input rotation.

[0030] The drive source 101 is a power source such as a motor. The power generated by the drive source 101 is transmitted to the input shaft 500 in the gear unit 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. This allows the drive source 101 to rotate the input shaft 500.

[0031] Furthermore, in the gear device 1 relating to this basic configuration, as shown in Figure 4, the input rotation axis Ax1 and the output rotation axis Ax1 are on the same straight line. In other words, the input rotation axis Ax1 and the output rotation axis Ax1 are coaxial. Here, the input rotation axis Ax1 is the rotation center of the input shaft 500 to which the input rotation is applied, and the output rotation axis Ax1 is the rotation center of the inner ring 61 (and a pair of carriers 18, 19) that generates the output rotation. In other words, in the gear device 1, an output rotation reduced at a relatively high reduction ratio relative to the input rotation is obtained on the same axis.

[0032] As shown in Figures 5 and 6, the internal gear 2 is an annular component having internal teeth 21. In this basic configuration, the 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 internal gear 2, along the circumferential direction of the internal gear 2. All of the teeth constituting the internal teeth 21 are of the same shape and are provided at equal pitches across the entire circumferential area of ​​the inner circumferential surface of the internal gear 2. In other words, the pitch circle of the internal teeth 21 is a perfect circle in plan view. The center of the pitch circle of the internal teeth 21 lies on the rotation axis Ax1. The internal gear 2 also has a predetermined thickness in the direction of the rotation axis Ax1. The tooth traces of the internal teeth 21 are all parallel to the rotation axis Ax1. The dimension of the internal teeth 21 in the direction of the tooth traces is slightly smaller than the thickness direction of the internal gear 2.

[0033] Here, the internal gear 2, as described above, has an annular (circular) gear body 22 and a plurality of external pins 23. The plurality of external pins 23 are held on the inner circumferential surface 221 of the gear body 22 in a state in which they can rotate, and constitute the internal teeth 21. In other words, the plurality of external pins 23 each function as a plurality of teeth that constitute the internal teeth 21. Specifically, as shown in Figure 2, a plurality of internal grooves 223 are formed on the inner circumferential surface 221 of the gear body 22 over the entire circumference. The plurality of internal grooves 223 are all the same shape and are provided at equal pitches. The plurality of internal grooves 223 are all parallel to the rotation axis Ax1 and are formed over the entire length of the gear body 22 in the thickness direction. The plurality of external pins 23 are assembled to the gear body 22 so as to fit into the plurality of internal grooves 223. Each of the plurality of external pins 23 is held in a state in which it can rotate within the internal groove 223. Furthermore, the gear body 22 is fixed to the case 10 (together with the outer ring 62). In addition, the gear body 22 has multiple fixing holes 222 (see Figure 5) for fixing.

[0034] As shown in Figures 5 and 6, the planetary gear 3 is an annular component having external teeth 31. In this basic configuration, the planetary gear 3 has an annular shape, with at least its outer circumferential surface being a perfect circle in plan view. The 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 of the teeth constituting the external teeth 31 are the same shape and are provided at equal pitches over the entire circumferential area of ​​the outer circumferential surface of the planetary gear 3. In other words, the pitch circle of the external teeth 31 is a perfect circle in plan view. The planetary gear 3 also has a predetermined thickness in the direction of the rotation axis Ax1. All of the external teeth 31 are formed along the entire length in the thickness direction of the planetary gear 3. The tooth traces of the external teeth 31 are all parallel to the rotation axis Ax1. In the planetary gear 3, unlike the internal gear 2, the external teeth 31 are integrally formed with the body of the planetary gear 3 from a single metal component.

[0035] Furthermore, the gear unit 1 in this basic configuration includes multiple planetary gears 3. Specifically, the gear unit 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. In other words, the planetary gear 3 includes a first planetary gear 301 and a second planetary gear 302 that are aligned in 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 the same.

[0036] These two planetary gears 3 (the first planetary gear 301 and the second planetary gear 302) are positioned with a 180-degree phase difference around the rotation axis Ax1. In the example in Figure 4, of the first planetary gear 301 and the second planetary gear 302, the center C1 (center of the pitch circle of the external teeth 31) of the first planetary gear 301, which is located on the input side of the rotation axis Ax1 (right side in Figure 4), is shifted (biased) upward relative to the rotation axis Ax1 in the figure. On the other hand, the center C2 (center of the pitch circle of the external teeth 31) of the second planetary gear 302, which is located on the output side of the rotation axis Ax1 (left side in Figure 4), is shifted (biased) downward relative to the rotation axis Ax1 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 with respect 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 with respect to the rotation axis Ax1. In this way, by arranging the multiple planetary gears 3 evenly in the circumferential direction around the rotation axis Ax1, it is possible to balance the weight and load among the multiple planetary gears 3.

[0037] The first planetary gear 301 and the second planetary gear 302 have centers C1 and C2 positioned 180 degrees rotationally symmetric with respect to the axis of rotation Ax1. In this basic configuration, the eccentricity ΔL1 and eccentricity ΔL2 are in opposite directions when viewed from the axis of rotation Ax1, but their absolute values ​​are the same.

[0038] More specifically, each crankshaft 7A, 7B, and 7C has two eccentric portions 72 with respect to one central axis 71. The eccentricity ΔL0 (see Figures 5 and 6) of the centers C0 of these two eccentric portions 72 from the center of the central axis 71 (axis Ax2) is the same as the eccentricity ΔL1 and ΔL2 of the first planetary gear 301 and the second planetary gear 302 with respect to the rotation axis Ax1, respectively. The shapes of the multiple crankshafts 7A, 7B, and 7C are common. Similarly, the shapes of the multiple crankshaft gears 502A, 502B, and 502C are also common.

[0039] Furthermore, a pair of carriers 18 and 19 are positioned 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). To distinguish between the pair of carriers 18 and 19, the carrier 18 located on the input side of the rotation axis Ax1 (right side in Figure 4) is called the "input side carrier 18," and the carrier 19 located on the output side of the rotation axis Ax1 (left side in Figure 4) is called the "output side carrier 19." Each crankshaft 7A, 7B, and 7C is held at both ends by the pair of carriers 18 and 19 via rolling bearings 41 and 42. In other words, each crankshaft 7A, 7B, and 7C is held by the input side carrier 18 and the output side carrier 19 in a state that allows it to rotate on both sides of the planetary gear 3 in the direction parallel to the rotation axis Ax1 (axial direction).

[0040] Eccentric bearings 5 ​​are mounted on the eccentric portions 72 of each crankshaft 7A, 7B, and 7C. Each of the first planetary gear 301 and the second planetary gear 302 has three openings 33 corresponding to the three crankshafts 7A, 7B, and 7C. Eccentric bearings 5 ​​are housed in each of the openings 33. In other words, eccentric bearings 5 ​​are attached to the first planetary gear 301 and the second planetary gear 302, and each crankshaft 7A, 7B, and 7C is inserted into the eccentric bearings 5, thereby assembling the eccentric bearings 5 ​​and each crankshaft 7A, 7B, and 7C into the planetary gear 3. When each crankshaft 7A, 7B, and 7C rotates in the state as the eccentric bearings 5 ​​and crankshafts 7A, 7B, and 7C are assembled into the planetary gear 3, the planetary gear 3 oscillates around the rotation axis Ax1.

[0041] According to the configuration described above, when a rotational force is applied as input to the input shaft 500, the input shaft 500 rotates around the rotation axis Ax1, and this rotational force is distributed from the input gear 501 to the 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 the input gear 501 simultaneously rotate in the same direction at the same rotational speed. Since the crankshafts 7A, 7B, and 7C are spline-connected 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 rotational speed while being reduced by the tooth ratio between the input gear 501 and the crankshaft gears 502A, 502B, and 502C. As a result, the three eccentric portions 72 formed at the same position on the input side of the rotation axis Ax1 on the three crankshafts 7A, 7B, and 7C rotate synchronously, causing the first planetary gear 301 to oscillate. Furthermore, the three eccentric portions 72 formed at the same position on the output side of the rotation axis Ax1 on the three crankshafts 7A, 7B, and 7C rotate synchronously, causing the second planetary gear 302 to oscillate.

[0042] Figures 5 and 6 show the state of the first planetary gear 301 and the second planetary gear 302 at a certain point in time. Figure 5 is a cross-sectional view taken along line A1-A1 in Figure 4, showing the first planetary gear 301. Figure 6 is a cross-sectional view taken along line B1-B1 in 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 positioned approximately 180 degrees rotationally symmetric with respect to the rotation axis Ax1. In this basic configuration, the eccentricity ΔL1 and eccentricity ΔL2 are in opposite directions when viewed from the rotation axis Ax1, but their absolute values ​​are approximately the same (both are eccentricity ΔL0). According to the above configuration, as the axial core 71 rotates (rotates) around the axis Ax2, the first planetary gear 301 and the second planetary gear 302 rotate (eccentrically) around the rotation axis Ax1 with a phase difference of approximately 180 degrees around the rotation axis Ax1. Furthermore, by arranging the multiple planetary gears 3 almost evenly in the circumferential direction around the rotation axis Ax1, it is possible to balance the weight and load among the multiple planetary gears 3.

[0043] The planetary gear 3 (first planetary gear 301 and second planetary gear 302) configured in this way is positioned inside the internal gear 2. In plan view, the planetary gear 3 is formed to be slightly smaller than the internal gear 2, and when combined with the internal gear 2, the planetary gear 3 is able to oscillate inside the internal gear 2. Here, 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, when the planetary gear 3 is positioned inside the internal gear 2, the external teeth 31 and the internal teeth 21 face each other.

[0044] Furthermore, the pitch circle of the external teeth 31 is slightly smaller than the pitch circle of the internal teeth 21. When the first planetary gear 301 is inscribed in the internal gear 2, the center C1 of the pitch circle of the external teeth 31 in the first planetary gear 301 is located at a distance ΔL1 from the center of the pitch circle of the internal teeth 21 (rotation axis Ax1). Similarly, when the second planetary gear 302 is inscribed in the internal gear 2, the center C2 of the pitch circle of the external teeth 31 in the second planetary gear 302 is located at a distance ΔL2 from the center of the pitch circle of the internal teeth 21 (rotation axis Ax1).

[0045] Therefore, in both the first planetary gear 301 and the second planetary gear 302, at least a portion of the external teeth 31 and internal teeth 21 will face each other with a gap in between, and if the difference in the number of teeth between the external teeth 31 and internal teeth 21 is "2" or more, the entire circumferential direction will not mesh with each other. However, since the planetary gear 3 oscillates (revolves) around the rotation axis Ax1 inside the internal gear 2, the external teeth 31 and internal teeth 21 will partially mesh. In other words, as the planetary gear 3 (first planetary gear 301 and second planetary gear 302) oscillates around the rotation axis Ax1, as shown in Figures 5 and 6, some of the teeth of the multiple teeth constituting the external teeth 31 will mesh with some of the teeth of the multiple teeth constituting the internal teeth 21. As a result, in the gear device 1, it is possible to mesh a portion of the external teeth 31 with a portion of the internal teeth 21.

[0046] Here, the number of teeth on the internal gear 21 is N (where N is a positive integer) greater than the number of teeth on the external gear 31 of the planetary gear 3. In this basic configuration, as an example, N is "2", and the number of teeth on the planetary gear 3 (external gear 31) is "2" less than the number of teeth on the internal gear 2 (internal gear 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 to the input rotation in the gear device 1.

[0047] Furthermore, in this basic configuration, 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. Moreover, the dimension of the external teeth 31 of the combined first planetary gear 301 and the second planetary gear 302 in the tooth trace direction (direction parallel to the rotation axis Ax1) is smaller than the dimension of the internal teeth 21 in the tooth trace direction (direction parallel to the rotation axis Ax1). 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 range of the tooth trace of the internal teeth 21.

[0048] 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, a circumferential phase shift occurs between them and the internal gear 2 equal to the difference in the number of teeth (between the internal teeth 21 and the external teeth 31), causing them to rotate. Due to this rotation, the first planetary gear 301 and the second planetary gear 302 revolve around the inner circumference of the internal gear 2 (i.e., they revolve around the axis of rotation Ax1) while partially meshing with the internal teeth 21 of the internal gear 2. Each crankshaft 7A, 7B, and 7C inserted into the opening 33 of the planetary gear 3 revolves around the axis of rotation Ax1 in conjunction with the revolution of the planetary gear 3. In this way, the revolution of the planetary gear 3 is transmitted to a pair of carriers 18 and 19 via multiple crankshafts 7A, 7B, and 7C. This allows the pair of carriers 18 and 19 to rotate relative to the gear body (and the integrated case 10) around the rotation axis Ax1.

[0049] In short, the gear device 1 in this basic configuration uses multiple crankshafts 7A, 7B, and 7C, positioned offset from the rotation axis Ax1, to oscillate a planetary gear 3, and obtains rotational output by utilizing the oscillation of the planetary gear 3. That is, in the gear device 1, as the planetary gear 3 oscillates and the meshing position between the internal teeth 21 and the external teeth 31 moves in the circumferential direction of the internal gear 2, relative rotation occurs between the two gears (internal gear 2 and planetary gear 3) according to the difference in the number of teeth between the planetary gear 3 and the internal gear 2. If the internal gear 2 is fixed, the planetary gear 3 will rotate (rotate on its own axis) in conjunction with the relative rotation of the two gears. As a result, rotational output reduced at a relatively high reduction ratio according to the difference in the number of teeth between the two gears can be obtained from the planetary gear 3.

[0050] The bearing member 6 has an outer ring 62 and an inner ring 61, and is a component for extracting 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 inner ring 61, the bearing member 6 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 have annular shapes that are perfect circles in plan view. The inner ring 61 is slightly smaller than the outer ring 62 and is positioned inside the outer ring 62. Here, since the inner diameter of the outer ring 62 is larger than the outer diameter of the inner ring 61, a gap is created between the inner circumferential surface of the outer ring 62 and the outer circumferential surface of the inner ring 61.

[0051] Multiple rolling elements 63 are arranged in the gap between the outer ring 62 and the inner ring 61. Multiple rolling elements 63 are arranged in a line along the circumference of the outer ring 62. All of the multiple rolling elements 63 are metal parts of the same shape and are provided at equal pitches over the entire circumference of the outer ring 62.

[0052] More specifically, the gear unit 1 in this basic configuration includes a first main bearing 601 and a second main bearing 602, which are bearing members 6, respectively. In other words, the gear unit 1 includes a pair of bearing members 6 consisting of a first main bearing 601 and a second main bearing 602. Specifically, as shown in Figure 4, the first main bearing 601 is positioned on the input side of the rotation axis Ax1 as viewed from the planetary gear 3 (right side in Figure 4), and the second main bearing 602 is positioned on the output side of the rotation axis Ax1 as viewed from the planetary gear 3 (left side in Figure 4). The pair of bearing members 6, the first main bearing 601 and the second main bearing 602, are configured to withstand radial loads, thrust loads (in the direction along the rotation axis Ax1), and bending forces (bending moment loads) on the rotation axis Ax1.

[0053] Here, the first bearing member 601 and the second bearing member 602 are positioned on both sides of the planetary gear 3 in a direction parallel to the rotation axis Ax1 (axial direction), and are facing opposite directions in a direction parallel to the rotation axis Ax1. In other words, the bearing member 6 is a "combined angular contact ball bearing" which is a combination of multiple (in this case, two) angular contact ball bearings. As an example, the first bearing member 601 and the second bearing member 602 are a "back-to-back combination type" which receives a thrust load (direction along the rotation axis Ax1) in which their respective inner rings 61 move closer to each other. Furthermore, in the gear device 1, the first bearing member 601 and the second bearing member 602 are combined in such a state that an appropriate preload is applied to the inner rings 61 by tightening them in a direction that brings their respective inner rings 61 closer to each other.

[0054] Furthermore, in the gear device 1 according to this basic configuration, the input carrier 18 and the output carrier 19 are arranged on both sides of the planetary gear 3 in a direction parallel to the rotation axis Ax1, and are coupled to each other through the carrier holes 34 of the planetary gear 3 (see Figure 4). Specifically, as shown in Figure 4, the input carrier 18 is positioned on the input side of the rotation axis Ax1 (right side in Figure 4) as viewed from the planetary gear 3, and the output carrier 19 is positioned on the output side of the rotation axis Ax1 (left side in Figure 4) as viewed from the planetary gear 3. The inner rings 61 of the bearing members 6 (each of the first bearing member 601 and the second bearing member 602) are fixed to the input carrier 18 and the output carrier 19. In this basic configuration, as an example, the inner ring of the first bearing member 601 is seamlessly integrated with the input carrier 18. Similarly, the inner ring of the second bearing member 602 is seamlessly integrated with the output carrier 19.

[0055] The output carrier 19 has a plurality of carrier pins 191 (see Figure 2) (three as an example) that protrude from one surface of the output carrier 19 toward the input side of the rotation axis Ax1. These plurality of carrier pins 191 each pass through a plurality of carrier holes 34 (three as an example) formed in the planetary gear 3, and their tips are fixed to the input carrier 18 by carrier bolts 192 (see Figure 7). Here, a gap is ensured between the carrier pins 191 and the inner circumferential surface of the carrier holes 34, and the carrier pins 191 are movable within the carrier holes 34, that is, they are movable relative to the center of the carrier holes 34. As a result, the carrier pins 191 do not come into contact with the inner circumferential surface of the carrier holes 34 when the planetary gear 3 oscillates.

[0056] With the above configuration, the gear unit 1 is used to extract the rotation equivalent to the rotation component of the planetary gear 3 as the rotation of the input carrier 18 and output carrier 19, which are integrated with the inner ring 61 of the bearing member 6. In other words, in this basic configuration, the relative rotation between the planetary gear 3 and the internal gear 2 is extracted from the input carrier 18 and output carrier 19. In this basic configuration, as an example, the gear unit 1 is used with the outer ring 62 (see Figure 4) of the bearing member 6 fixed to the case 10, which is a fixed member. That is, the planetary gear 3 is connected to the input carrier 18 and output carrier 19, which are rotating members, by 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 extracted from the rotating members (input carrier 18 and output carrier 19). In other words, in this basic configuration, when the planetary gear 3 rotates relative to the gear body 22, the rotational forces of the input carrier 18 and the output carrier 19 are extracted as outputs.

[0057] Furthermore, in this basic configuration, the case 10 is seamlessly integrated with the gear body 22 of the internal gear 2. In other words, in a direction parallel to the rotation axis Ax1, the fixed member, the gear body 22, and the case 10 are provided seamlessly and continuously.

[0058] More specifically, the case 10 is cylindrical and constitutes the outer casing of the gear unit 1. In this basic configuration, the central axis of the cylindrical case 10 is configured to coincide with the rotation axis Ax1. That is, at least the outer surface of the case 10 is a perfect circle centered on the rotation axis Ax1 when viewed from a plan view (viewed from one side in the axial direction). The case 10 is formed in a cylindrical shape with both axial end faces open. Here, the gear body 22 of the internal gear 2 is seamlessly integrated into the case 10, and the case 10 and the gear body 22 are treated as a single part. Therefore, the inner surface of the case 10 includes the inner surface 221 of the gear body 22. Furthermore, the outer ring 62 of the bearing member 6 is fixed to the case 10. That is, the outer ring 62 of the first bearing member 601 is fitted and fixed to the input side of the rotation axis Ax1 (right side in Figure 4) when viewed from the gear body 22 on the inner surface of the case 10. On the other hand, the outer ring 62 of the second bearing member 602 is fitted and fixed to the output side (left side in Figure 4) of the rotating shaft Ax1 as seen from the gear body 22 on the inner circumferential surface of the case 10.

[0059] Furthermore, the input side (right side in Figure 4) end face of the rotating shaft Ax1 in case 10 is closed by the input side carrier 18, and the output side (left side in Figure 4) end face of the rotating shaft Ax1 in case 10 is closed by the output side carrier 19. As a result, as shown in Figure 4, components such as the planetary gear 3 (first planetary gear 301 and second planetary gear 302), multiple external pins 23, and eccentric bearing 5 are housed in the space enclosed by case 10, the input side carrier 18, and the output side carrier 19.

[0060] Each of the multiple (three in the basic configuration) crankshafts 7A, 7B, and 7C has an axial core 71 and two eccentric parts 72. The axial core 71 has a cylindrical shape, with at least its outer surface being a perfect circle in plan view. The axis Ax2, which is the center of the axial core 71, is parallel to the rotation axis Ax1. The axis 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 part 72 has a disc shape, with at least its outer surface being a perfect circle in plan view. The center (central axis) C0 of each eccentric part 72 is parallel to the rotation axis Ax1 and is positioned radially offset from the rotation axis Ax1. Here, the distance ΔL0 between the axis Ax2 and the center C0 (see Figures 5 and 6) is the amount of eccentricity of the eccentric part 72 relative to the axial core 71. The eccentric portion 72 has a flange shape that protrudes from the outer circumferential surface of the shaft portion 71 around its entire circumference at the center of the shaft portion 71 in the longitudinal direction (axial direction). With the above configuration, each crankshaft 7A, 7B, and 7C will undergo eccentric motion as the shaft portion 71 rotates around the shaft Ax2.

[0061] In this basic configuration, the central shaft 71 and the two eccentric shafts 72 are integrally formed from a single metal component, thereby realizing seamless crankshafts 7A, 7B, and 7C. These crankshafts 7A, 7B, and 7C are combined with the planetary gear 3 along with the eccentric bearing 5. Therefore, when the crankshafts 7A, 7B, and 7C rotate with the planetary gear 3 assembled to the eccentric bearing 5, the planetary gear 3 oscillates around the rotation axis Ax1.

[0062] The eccentric bearing 5 has multiple rolling elements 51 (see Figure 4) and is a component that absorbs the rotational component of the rotation of the crankshafts 7A, 7B, and 7C, and transmits only the rotational component (orbital component) of the crankshafts 7A, 7B, and 7C to the planetary gear 3. The multiple rolling elements 51 are arranged between the outer circumferential surface of the eccentric portion 72 of each crankshaft 7A, 7B, and 7C and the inner circumferential surface of each opening 33 of the planetary gear 3. In other words, the eccentric portion 72 of each crankshaft 7A, 7B, and 7C functions as the inner ring of the eccentric bearing 5, and the inner circumferential surface of each opening 33 of the planetary gear 3 functions as the outer ring of the eccentric bearing 5.

[0063] With the eccentric bearing 5 and multiple crankshafts 7A, 7B, and 7C assembled to the planetary gear 3, when each crankshaft 7A, 7B, and 7C rotates (rotates), each eccentric part 72 rotates (performs eccentric motion) around the axis Ax2. Since the planetary gear 3 is installed in a direction parallel to the rotation axis Ax1 (axial direction) corresponding to each eccentric part 72, 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 on the crankshafts 7A, 7B, and 7C is transmitted to the planetary gear 3. The eccentric bearing 5 plays a role in mitigating friction and other issues caused by relative rotation resulting from the speed difference between the eccentric motion of the eccentric portion 72 of each crankshaft 7A, 7B, and 7C (i.e., the rotation of each crankshaft 7A, 7B, and 7C) and the revolution of the planetary gear 3, as well as in power transmission.

[0064] In the gear device 1 with the configuration described above, a rotational force is applied as input to the input shaft 500, causing the input shaft 500 to rotate around the rotation axis Ax1, and the planetary gear 3 oscillates (revolves) around the rotation axis Ax1. At this time, the planetary gear 3 oscillates inside the internal gear 2, with a portion of the external teeth 31 meshing with a portion of the internal teeth 21. As the input shaft 500 rotates, the meshing position between the internal teeth 21 and the external teeth 31 moves in the circumferential direction 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. The rotation (rotation component) of the planetary gear 3, excluding the oscillating component (revolution component), is transmitted to the pair of carriers 18 and 19 by multiple crankshafts 7A, 7B, and 7C. As a result, the pair of carriers 18 and 19 will produce rotational output that is reduced at a relatively high reduction ratio, depending on the difference in the number of teeth of the two gears.

[0065] Incidentally, in the gear unit 1 relating to this basic configuration, as described above, the difference in the number of teeth between the internal gear 2 and the planetary gear 3 determines the reduction ratio of the output rotation to the input rotation in the gear unit 1. In other words, if the number of teeth of the internal gear 2 is "V1" and the number of teeth of the planetary gear 3 is "V2", the reduction ratio R1 is expressed by the following equation 1.

[0066] R1 = V2 / (V1 - V2) (Equation 1) In short, the smaller the difference in the number of teeth between the internal gear 2 and the planetary gear 3 (V1-V2), the larger the reduction ratio R1. For 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", so from equation 1 above, the reduction ratio R1 is "35". In this case, when viewed from the input side of the rotation axis Ax1, each crankshaft 7A, 7B, 7C rotates clockwise one full turn (360 degrees) around the axis Ax2 of the shaft center 71 (see Figures 5 and 6), the pair of carriers 18, 19 rotate counterclockwise around the rotation axis Ax1 by the amount of the difference in the number of teeth "2" (i.e., about 10.3 degrees).

[0067] According to the gear unit 1 of this basic configuration, such a high reduction ratio R1 can be achieved with 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 be achieved depending 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 for the gear unit 1 as a whole.

[0068] Furthermore, the gear unit 1 only needs to include at least an internal gear 2, planetary gears 3, crankshafts 7A, 7B, 7C, and a pair of carriers 18, 19, and may further include a spacer 11, for example, as shown in Figure 4. The spacer 11 is positioned between the pair of planetary gears 3 (first planetary gear 301 and second planetary gear 302) in a direction parallel to the rotation axis Ax1 (axial direction).

[0069] (Embodiment 1) As shown in Figures 7 to 9, the internally meshing planetary gear device 1A according to this embodiment (hereinafter also simply referred to as "gear device 1A") differs from the gear device 1 in the basic configuration mainly in the configuration of the planetary gears 3 (first planetary gear 301 and second planetary gear 302). Hereafter, components similar to those in the basic configuration will be denoted by common reference numerals and their descriptions will be omitted as appropriate.

[0070] In this embodiment, an internal planetary gear system using a trochoidal tooth profile is presented as an example of a gear system 1A. That is, the gear system 1A according to this embodiment is equipped with an internal planetary gear 3 having a trochoidal curved tooth profile. Here, the gear system 1A is equipped with two planetary gears 3, a first planetary gear 301 and a second planetary gear 302, similar to the basic configuration. The two planetary gears 3 are arranged in a direction parallel to the rotation axis Ax1 (axial direction) and are positioned with a phase difference of 180 degrees around the rotation axis Ax1. Since the shapes of the first planetary gear 301 and the second planetary gear 302 are common, the configuration of the planetary gear 3 will be described below using the first planetary gear 301 as an example.

[0071] In the gear assembly 1A according to this embodiment, the following conditions are met with respect to 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, both the number of teeth of the internal teeth 21 and the number of teeth of the external teeth 31 are odd, and the difference in the number of teeth between the internal teeth 21 and the external teeth 31 is "2".

[0072] Specifically, the tooth profile of the external teeth 31 of the planetary gear 3 is represented using a trochoidal curve TC1, for example, as shown in Figure 7. The trochoidal curve TC1 illustrated in Figure 7 is the trajectory traced by a point set within a rotating circle that rolls smoothly around the outer circumference of the base circle, with the diameter ratio of the base circle to the rotating circle being a non-integer (for example, "13 / 2"), such that the rotating circle returns to its starting point after rolling around the outer circumference of the base circle twice.

[0073] Then, as shown in Figure 8, the innermost curve portion (the thick line portion in Figure 8) of the two-part trochoid curve TC1 is adopted as the tooth profile curve of the external teeth 31 of the planetary gear 3. This realizes a planetary gear 3 with an odd number of teeth on the external teeth 31 (13 in the example in Figure 8). The number of teeth on the external teeth 31, which are formed from the trochoid curve TC1 set so that the rotation circle returns to the starting point after rolling around the outer circumference of the base circle twice, will always be odd. In Figure 8, the portion of the external teeth 31 formed on the outer circumference of the planetary gear 3 is shown as a shaded area.

[0074] As shown in Figure 9, the planetary gear 3, which has external teeth 31 with the tooth profile described above, meshes with the internal teeth 21 of the internal gear 2. Here, the number of external pins 23 that make up the internal teeth 21 is two more than the number of teeth on the external teeth 31. In other words, the number of teeth on the internal teeth 21 of the internal gear 2 is "15", which is "2" more than the number of teeth on the external teeth 31 of the planetary gear 3 (in this case, "13"). Therefore, not only the number of teeth on the external teeth 31 but also the number of teeth on the internal teeth 21 is odd (in the example in Figure 9, it is "15"). Furthermore, the difference in the number of teeth between the internal teeth 21 and the external teeth 31 is "2".

[0075] In this embodiment, the tooth profile curve of the external teeth 31 of the planetary gear 3 is located on the trochoidal curve TC1, and the planetary gear 3 oscillates (eccentrically rotates) inside the internal gear 2, which has an arc tooth profile that is two times greater than the number of teeth of the external teeth 31. As a result, as shown in Figure 9, the external teeth 31 and the internal teeth 21 face each other with at least a portion of them separated by a gap, and because the difference in the number of teeth between the external teeth 31 and the internal teeth 21 is "2", the entire circumferential direction does not mesh with each other.

[0076] In this way, the planetary gear 3 oscillates (revolves) around the rotation axis Ax1 inside the internal gear 2, so that the external teeth 31 and the internal teeth 21 partially mesh. In other words, as the planetary gear 3 oscillates around the rotation axis Ax1, some of the teeth that make up the external teeth 31 mesh with some of the teeth that make up the internal teeth 21. As a result, in the gear device 1A, it is possible to mesh some of the external teeth 31 with some of the internal teeth 21.

[0077] Figures 7 to 9 show a specific example where the number of teeth in the internal teeth 21 and the number of teeth in the external teeth 31 are both odd, and the difference in the number of teeth between the internal teeth 21 and the external teeth 31 is "2". In this example, the number of teeth in the external teeth 31 is "13" and the number of teeth in the internal teeth 21 is "15". However, the number of teeth in the internal teeth 21 and the number of teeth in the external teeth 31 are not limited to this example. For example, if a trochoid curve is used in which the diameter ratio of the base circle to the rotating circle is "23 / 2", and the rotating circle returns to the starting point when it rolls around the outer circumference of the base circle twice, the number of teeth in the external teeth 31 will be "23" and the number of teeth in the internal teeth 21 will be "25".

[0078] Next, with reference to Figures 10 and 11, a comparative example gear assembly 1X (see Figure 11) will be described. In the comparative example gear assembly 1X, with respect to 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, instead of the conditions of this embodiment, the number of teeth of the internal teeth 21 and the number of teeth of the external teeth 31 are both even, and the difference in the number of teeth between the internal teeth 21 and the external teeth 31 is "2".

[0079] Specifically, in the comparative example, the tooth profile of the external teeth 31 of the planetary gear 3 is represented using two trochoidal curves TC11 and TC12, as shown in Figure 10. Each of the trochoidal curves TC11 and TC12 exemplified in Figure 10 is the trajectory traced by a point set within a rotating circle that rolls smoothly around the outer circumference of the base circle, with the diameter ratio of the base circle to the rotating circle being an integer (for example, "11"), such that the rotating circle returns to its starting point after rolling around the outer circumference of the base circle once.

[0080] Then, as shown in Figure 11, these two trochoidal curves TC11 and TC12 are superimposed with a phase shift, and the innermost curve portion (the thick line portion in Figure 11) is adopted as the tooth profile curve of the external teeth 31 of the planetary gear 3. In the examples in Figures 10 and 11, each trochoidal curve TC11 and TC12 has "11" peaks, which is the diameter ratio of the base circle to the revolve. These two trochoidal curves TC11 and TC12 are superimposed with a phase shift of 180 degrees, or by the pitch of one peak, so that the peaks and valleys overlap.

[0081] This results in a planetary gear 3 with an even number of teeth on the external teeth 31 (20 in the example in Figure 11). The number of teeth on the external teeth 31, which are formed by the superposition of two trochoid curves TC11 and TC12 set so that the rotating circle returns to the starting point when it rolls around the outer circumference of the base circle once, is always even. In Figure 11, the portion of the external teeth 31 formed on the outer circumference of the planetary gear 3 is shown as a shaded area.

[0082] In the internal gear 2 paired with the planetary gear 3 having the external teeth 31 with the tooth profile described above, the number of external pins 23 constituting the internal teeth 21 is two more than the number of teeth on the external teeth 31. In other words, the number of teeth on the internal teeth 21 of the internal gear 2 is "22", which is "2" more than the number of teeth on the external teeth 31 of the planetary gear 3 (here, "20"). Therefore, both the number of teeth on the external teeth 31 and the number of teeth on the internal teeth 21 are even.

[0083] In a configuration like the gear apparatus 1X in the comparative example above, where both the number of teeth of the internal teeth 21 and the number of teeth of the external teeth 31 are even, the external teeth 31 are formed by the superposition of two trochoid curves TC11 and TC12. Therefore, no adjacent pairs of teeth on the external teeth 31 share teeth with the teeth of the internal teeth 21 that they mesh with. Consequently, each time the input shaft 500 rotates around the rotation axis Ax1 by the reduction ratio (e.g., "11") and the planetary gear 3 rotates once, the same teeth mesh between the external teeth 31 and the internal teeth 21 occurs. As a result, in the gear apparatus 1X in the comparative example, if damage (surface-initiated flaking) occurs between the external teeth 31 and the internal teeth 21, starting from an indentation caused by foreign matter such as wear particles, a combination of meshing that leads to the growth of surface-initiated flaking occurs each time the planetary gear 3 rotates once, and the damage may progress relatively quickly.

[0084] In contrast, in a configuration like the gear unit 1A according to this embodiment, where both the number of teeth of the internal teeth 21 and the number of teeth of the external teeth 31 are odd, the external teeth 31 are originally made up of a single offset trochoid curve TC1. Therefore, adjacent pairs of teeth on the external teeth 31 share teeth with the teeth of the internal teeth 21 that they mesh with. As a result, the same teeth mesh between the external teeth 31 and the internal teeth 21 only occurs after the input shaft 500 rotates around the rotation axis Ax1 by twice the reduction ratio (e.g., "11.5") (e.g., "23") and the planetary gear 3 has rotated twice. Consequently, in the gear unit 1A according to this embodiment, if damage occurs between the external teeth 31 and the internal teeth 21, starting from an indentation caused by foreign matter such as wear particles, a combination of meshing that would lead to surface-started damage will not occur until the planetary gear 3 has rotated twice. Therefore, compared to the comparative example above, the progression of damage is slowed by half, and the lifespan of the gear unit 1A can be extended by approximately double.

[0085] As described above, the gear device 1A according to this embodiment comprises 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 is the axis of the internal gear 2, and are driven synchronously by the input gear 501. The gear device 1A is an internal meshing planetary gear device that rotates the planetary gear 3 relative to the internal gear 2 around the rotation axis Ax1 by oscillating the planetary gear 3 with the plurality of eccentric shafts. Here, 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 in the number of teeth between the internal teeth 21 and the external teeth 31 is 2.

[0086] With this configuration, even if damage occurs between the external teeth 31 and the internal teeth 21, for example, starting from an indentation caused by foreign matter getting caught, it is possible to slow down the progression of such damage, and a gear device 1A that is less prone to a decrease in reliability can be provided. Furthermore, the gear device 1A according to this embodiment is less prone to a decrease in reliability, especially during long-term use, which in turn leads to improved transmission efficiency, longer lifespan, and higher performance of the gear device 1A.

[0087] Furthermore, in this embodiment, the gear unit 1A has a first planetary gear 301 and a second planetary gear 302. That is, the gear unit 1A further includes a second planetary gear 302 having a second external tooth that partially meshes with the internal tooth 21, in addition to the first planetary gear 301, which is a planetary gear 3 having a first external tooth as an external tooth 31. The eccentric shafts (crankshafts 7A, 7B, 7C) cause the first planetary gear 301 and the second planetary gear 302 to oscillate and rotate, respectively.

[0088] In this way, by providing multiple planetary gears 3 (first planetary gear 301 and second planetary gear 302), the gear device 1A can balance the weight and load among the multiple planetary gears 3. Furthermore, for each planetary gear 3 (first planetary gear 301 and second planetary gear 302), it is possible to slow down the progression of damage starting from the indentation between the external teeth 31 and the internal teeth 21.

[0089] Furthermore, the number of teeth on the second external tooth is the same as the number of teeth on the first external tooth. In other words, 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.

[0090] As a result, both the first planetary gear 301 and the second planetary gear 302 can satisfy the same conditions regarding their relationship with the internal gear 2 (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 in the number of teeth between the internal teeth 21 and the external teeth 31 is "2"). Consequently, in both the first planetary gear 301 and the second planetary gear 302, it is possible to slow down the progression of damage starting from the indentation between the external teeth 31 and the internal teeth 21.

[0091] Furthermore, in the gear device 1A according to this embodiment, the internal gear 2 has an annular gear body 22 and a plurality of external pins 23 that constitute the internal teeth 21. The plurality of external pins 23 are held in a rotatable state in a plurality of internal grooves 223 formed on the inner circumferential surface 221 of the gear body 22.

[0092] As a result, even if damage originating from indentations occurs between the outer tooth 31 and the inner tooth 21 due to irregularities on the surface of the multiple outer pins 23 constituting the inner tooth 21, it is possible to slow down the progression of such damage.

[0093] Incidentally, as shown in Figure 12, the gear device 1A according to this embodiment, together with the first member 201 and the second member 202, constitutes a robot joint device 200. In other words, the robot joint device 200 according to this embodiment comprises the gear device 1A, the first member 201, and the second member 202. The first member 201 is fixed to the internal gear 2. The second member 202 rotates relative to the first member 201 in accordance with the relative rotation of the planetary gear 3 with respect to the internal gear 2. Figure 12 is a schematic cross-sectional view of the robot joint device 200. Also, Figure 12 schematically shows the first member 201, the second member 202, and the drive source 101.

[0094] The robot joint device 200 configured in this way functions as a joint device by the relative rotation of the first member 201 and the second member 202 around the rotation axis Ax1. Here, the input shaft 500 of the gear device 1A is driven by the drive source 101, causing the first member 201 and the second member 202 to rotate relative to each other. At this time, the rotation (input rotation) generated by the drive source 101 is reduced by the gear device 1A at a relatively high reduction ratio, driving the first member 201 or the second member 202 with relatively high torque. In other words, the first member 201 and the second member 202, which are connected by the gear device 1A, are able to perform bending and extending movements around the rotation axis Ax1.

[0095] The robot joint device 200 is used in robots such as horizontal articulated robots (SCARA type robots). Furthermore, the robot joint device 200 is not limited to horizontal articulated robots, but may also be used in industrial robots other than horizontal articulated robots, or in robots other than industrial robots. In addition, the gear device 1A according to this embodiment is not limited to the robot joint device 200, but may also be used as a wheel device such as an in-wheel motor in vehicles such as automated guided vehicles (AGVs).

[0096] <Variation> 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.

[0097] The number of crankshafts 7A, 7B, and 7C is not limited to "3"; it may be 2 or 4 or more. Furthermore, if there is only one crankshaft, an eccentric oscillating internal meshing planetary gear system can be realized where the rotation axis Ax1 and the axis Ax2 of the crankshaft coincide, rather than a distribution type. In this case, the planetary gear 3 oscillates when the crankshaft is driven, and the pair of carriers 18 and 19 can be rotated relative to the gear body 22 around the rotation axis Ax1.

[0098] Furthermore, while Embodiment 1 illustrates two types of gear systems 1A with planetary gears 3, a gear system 1A may have three or more planetary gears 3. For example, if a gear system 1A has 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, a gear system 1A may have only one planetary gear 3. Or, if a gear system 1A has three planetary gears 3, two of these three planetary gears 3 may be in phase, and the remaining planetary gear 3 may be arranged with a phase difference of 180 degrees around the rotation axis Ax1.

[0099] Furthermore, the bearing member 6 may be a cross roller bearing, a deep groove ball bearing, a four-point contact ball bearing, or the like.

[0100] 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 external pins 23 (number of teeth of internal teeth 21), and the number of teeth of external teeth 31 described in Embodiment 1 are merely examples and can be changed as appropriate.

[0101] Furthermore, the eccentric bearing 5 is not limited to a roller bearing; for example, it may be a deep groove ball bearing or an angular contact ball bearing.

[0102] Furthermore, the material of each component of the gear unit 1A is not limited to metal; for example, it may be a resin such as engineering plastic.

[0103] Furthermore, the gear unit 1A only needs to be able 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 a configuration in which the rotational force of the inner ring 61 (input carrier 18 and output carrier 19) is output. For example, the rotational force of the outer ring 62 (case 10) that rotates relative to the inner ring 61 may be output.

[0104] Furthermore, the lubricant is not limited to liquid substances such as lubricating oil, but may also be a gel-like substance such as grease.

[0105] (summary) As described above, the internal meshing planetary gear device (1,1A) according to the first embodiment comprises 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 is the axis of the internal gear (2), and are driven synchronously by an input gear (501). The internal meshing planetary gear device (1,1A) is an internal meshing planetary gear device that rotates the planetary gear (3) relative to the internal gear (2) around the rotation axis (Ax1) by oscillating the planetary gear (3) on the plurality of eccentric shafts. The number of teeth in both the internal teeth (21) and the external teeth (31) is odd, and the difference in the number of teeth between the internal teeth (21) and the external teeth (31) is 2.

[0106] According to this embodiment, even if damage occurs between the external teeth (31) and internal teeth (21), for example, starting from an indentation caused by the intrusion of a foreign object, it is possible to slow down the progression of such damage, and an internally meshing planetary gear device (1,1A) that is less prone to a decrease in reliability can be provided. Therefore, an internally meshing planetary gear device (1,1A) can be realized in which damage starting from an indentation between the external teeth (31) and internal teeth (21) is less likely to progress.

[0107] The internally meshing planetary gear device (1,1A) according to the second embodiment further comprises a second planetary gear (302) having second external teeth that partially mesh with the internal teeth (21), in addition to the first planetary gear (301) having first external teeth as external teeth (31) as a planetary gear (3) in the first embodiment. The eccentric shafts (crankshafts 7A,7B,7C) oscillate the first planetary gear (301) and the second planetary gear (302), respectively.

[0108] According to this embodiment, the internally meshing planetary gear system (1,1A) is capable of balancing the weight and load between the multiple planetary gears (3). Furthermore, for each of the first planetary gear (301) and the second planetary gear (302), it is possible to slow down the progression of damage starting from the indentation between the external teeth (31) and the internal teeth (21).

[0109] In the third embodiment of the internally meshing planetary gear device (1,1A), the number of teeth of the second external teeth is the same as the number of teeth of the first external teeth, as in the second embodiment.

[0110] According to this embodiment, the same conditions can be met in relation to the internal gear (2) in both the first planetary gear (301) and the second planetary gear (302) (the number of teeth of both the internal teeth (21) and the external teeth (31) are odd, and the difference in the number of teeth between the internal teeth (21) and the external teeth (31) is "2"). As a result, in both the first planetary gear (301) and the second planetary gear (302), it is possible to slow down the progression of damage starting from the indentation between the external teeth (31) and the internal teeth (21).

[0111] The internal meshing planetary gear device (1,1A) according to the fourth embodiment, in any of the first to third embodiments, has an internal gear (2) comprising an annular gear body (22) and a plurality of external pins (23) constituting internal teeth (21). The plurality of external pins (23) are held in a rotatable state in a plurality of internal grooves (223) formed on the inner circumferential surface (221) of the gear body (22).

[0112] According to this embodiment, for example, even if damage originating from an indentation occurs between the outer tooth (31) and the inner tooth (21) due to irregularities on the surface of the multiple outer pins (23) constituting the inner tooth (21), it is possible to slow down the progression of such damage.

[0113] A robot joint device (200) according to the fifth embodiment comprises an internal meshing planetary gear device (1,1A) according to any of the first to fourth embodiments, a first member (201) fixed to an internal gear (2), and a second member (202) that rotates relative to the first member (201) in accordance with the relative rotation of the planetary gear (3) with respect to the internal gear (2).

[0114] According to this embodiment, a robotic joint device (200) can be realized in which damage originating from indentations between the external teeth (31) and internal teeth (21) is less likely to progress.

[0115] The configurations relating to the second to fourth aspects are not essential to the internally meshing planetary gear unit (1,1A) and can be omitted as appropriate. [Explanation of symbols]

[0116] 1,1A Internally meshing planetary gear system 2 Internal gear 3 Planetary gears 7A, 7B, 7C Crankshaft (Eccentric Shaft) 21 Inner teeth 22 Gear body 23 Outer pin 31 External teeth (1st external tooth, 2nd external tooth) 200 Robot Joint Devices 201 First Member 202 Second Member 221 Inner surface 223 Inner circumferential groove 301 First Planetary Gear 302 Second Planetary Gear 501 Input Gear Ax1 Rotation axis

Claims

1. A robotic mechanical arm structure equipped with a robotic joint device, The aforementioned robot joint device is An internal gear having internal teeth, A planetary gear having external teeth that partially mesh with the internal teeth, The system comprises a plurality of eccentric shafts positioned at an offset location from the rotational axis which is the axis of the internal gear, and driven synchronously by an input gear, An internal meshing planetary gear device in which the planetary gear is rotated relative to the internal gear around the rotation axis by oscillating the planetary gear on the plurality of eccentric shafts, The number of teeth in the internal teeth and the number of teeth in the external teeth are both odd numbers. An internally meshing planetary gear mechanism in which the difference in the number of teeth between the internal teeth and the external teeth is 2, A first member fixed to the internal gear, The system comprises a second member that rotates relative to the first member in accordance with the relative rotation of the planetary gear with respect to the internal gear, Robotic mechanical arm structure.

2. An internal gear having internal teeth, A planetary gear having external teeth that partially mesh with the internal teeth, The system comprises a plurality of eccentric shafts positioned at an offset location from the rotational axis which is the axis of the internal gear, and driven synchronously by an input gear, An internal meshing planetary gear device in which the planetary gear is rotated relative to the internal gear around the rotation axis by oscillating the planetary gear on the plurality of eccentric shafts, The number of teeth in the internal teeth and the number of teeth in the external teeth are both odd numbers. The difference in the number of teeth between the internal teeth and the external teeth is 2. Internally meshing planetary gear system.

3. In addition to the first planetary gear having the first external teeth as external teeth, the planetary gear further comprises a second planetary gear having a second external tooth that partially meshes with the internal teeth, The eccentric shaft causes the first planetary gear and the second planetary gear to oscillate and rotate, The internal meshing planetary gear device according to claim 2.

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

5. The internal gear comprises an annular gear body and a plurality of external pins that are held in a rotatable state in a plurality of internal grooves formed on the inner surface of the gear body and constitute the internal teeth. An internal meshing planetary gear device according to any one of claims 2 to 4.

6. An internal meshing planetary gear device according to any one of claims 2 to 4, A first member fixed to the internal gear, The system comprises a second member that rotates relative to the first member in accordance with the relative rotation of the planetary gear with respect to the internal gear, Joint device for robots.

Images