Gear reduction mechanism

Abstract

To increase a gear reduction ratio while achieving size reduction in a gear reduction mechanism.SOLUTION: A gear reduction mechanism 30 comprises: a rotating shaft 10; a pinion gear 11 having a first tooth part 11a spirally extending along a longitudinal direction Q1 of the rotating shaft 10; three planetary gears 12 each having a spiral second tooth part 12e and aligned in a circumferential direction Q2 of the rotating shaft 10; an accommodation part 14 for accommodating the three planetary gears 12; and an inner gear 13 having a spiral third tooth part 13a engaged with the second tooth part 12e. The first tooth part 11a is at least partially formed into a circular shape in a tooth-shape cross section, and the second tooth part 12e is engaged with the first tooth part 11a in a state that the tooth shape cross section is in contact with circular portion.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a reduction mechanism using a planetary gear. [Background technology]

[0002] As an example of a reduction mechanism using planetary gears, Patent Document 1 shows a reduction mechanism having a sun gear, three planetary gears each meshing with the sun gear and rotating while revolving around the sun gear, and a fixed internal gear meshing with the three planetary gears. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-90792 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the reduction mechanism described in Patent Document 1 above, there is a demand for ensuring even greater output torque while maintaining a compact size, and therefore it is necessary to increase the reduction ratio while maintaining the compactness of the reduction mechanism.

[0005] In the case of the reduction gear mechanism of Patent Document 1, if it is desired to further increase the reduction ratio, it becomes necessary to reduce the number of planetary gears, which reduces the strength of the reduction gear mechanism.

[0006] On the other hand, if an attempt is made to ensure the strength of the reduction mechanism by reducing the number of planetary gears, the diameter of each planetary gear must be increased, which raises concerns that the reduction mechanism will become larger.

[0007] An object of the present invention is to provide a reduction mechanism that can increase the reduction ratio while achieving miniaturization. [Means for solving the problem]

[0008] One aspect of the present invention comprises a rotating shaft, a first gear provided on the outer periphery of the rotating shaft and having a first tooth portion extending spirally along the longitudinal direction of the rotating shaft, a plurality of second gears arranged side by side in the circumferential direction of the rotating shaft, each of the second gears having a spiral second tooth portion that meshes with the first tooth portion, a storage portion that houses the plurality of second gears, and a third gear provided on the inner periphery of the storage portion and having a spiral third tooth portion that meshes with the second tooth portion, wherein at least a portion of the first tooth portion has a tooth cross section formed in an arc shape, and the second tooth portion meshes with the first tooth portion while being in contact with a portion of the tooth cross section that is arc-shaped.

[0009] In another aspect of the present invention, at least three of the second gears are arranged side by side in the circumferential direction of the rotating shaft.

[0010] In another aspect of the present invention, when the pitch circle radius of the second gear is R1, the center-to-center distance from the center of rotation of the rotation shaft to the center of rotation of the second gear is L1, and the angle calculated by the formula (180° (sum of the interior angles of a triangle) - 90°) - (360° ÷ number of second gears ÷ 2) is θ, the pitch circle radius R1 < (center-to-center distance L1 × cos θ). Effect of the Invention

[0011] In the reduction mechanism, the reduction ratio can be increased while achieving a reduction in size. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is an external perspective view illustrating the structure of the reduction mechanism according to the present invention. [Diagram 2] 2 is a cross-sectional view illustrating the internal structure of the reduction mechanism in FIG. 1. [Diagram 3] 2 is an internal plan view illustrating the arrangement of a planetary gear (second gear) of the reduction mechanism in FIG. 1. FIG. [Figure 4] 2 is a perspective view illustrating a meshing state between a sun gear and a planetary gear and a meshing state between the planetary gear and a fixed internal gear (third gear) in the reduction gear mechanism of FIG. 1. [Diagram 5]2 is an external perspective view illustrating the structure of a sun gear (first gear) of the reduction mechanism in FIG. 1. [Figure 6] 2 is a plan view illustrating the structure of a planetary gear (second gear) of the reduction mechanism in FIG. 1. [Figure 7] FIG. 2 is a diagram for explaining a calculation of a non-interference condition between gears in a structure in which three planetary gears are provided in the reduction gear mechanism of FIG. 1. [Figure 8] FIG. 2 is a diagram for explaining a calculation of a non-interference condition between gears in a structure in which four planetary gears are provided in the reduction gear mechanism of FIG. 1. [Figure 9] FIG. 11 is a plan view illustrating a pitch circle diameter of an involute gear as a comparative example. [Figure 10] 2 is a perspective view illustrating a structure of a robot which is an application example of the reduction gear mechanism of FIG. 1. [Figure 11] 11 is an internal structural view for explaining an application structure of the reduction gear mechanism of FIG. 1 in the robot of FIG. 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0014] Fig. 1 is an external perspective view explaining the structure of the reduction mechanism of this embodiment, Fig. 2 is a cross-sectional view explaining the internal structure of the reduction mechanism of Fig. 1, and Fig. 3 is an internal plan view explaining the arrangement of the planetary gear (second gear) of the reduction mechanism of Fig. 1. Furthermore, Fig. 4 is an external perspective view explaining the structure of the sun gear (first gear) of the reduction mechanism of Fig. 1, Fig. 5 is a plan view explaining the structure of the planetary gear (second gear) of the reduction mechanism of Fig. 1, and Fig. 6 is a perspective view explaining the meshing state of the sun gear and planetary gear and the meshing state of the planetary gear and fixed internal gear (third gear) in the reduction mechanism of Fig. 1.

[0015] The reduction gear mechanism 30 of this embodiment is a mechanism capable of slowing down the rotation of the output shaft 15, which rotates together with the revolution of the planetary gears 12, relative to the rotation of the input shaft, by causing three or more planetary gears 12, which are each meshed with the sun gear and a fixed internal gear, to revolve due to the rotation of a sun gear provided on the rotating shaft 10, which is the input shaft.

[0016] The structure of the reduction gear mechanism 30 will be described with reference to Figs. 1 to 6. First, a case where three planetary gears 12 are provided will be described. As shown in Figs. 3 and 4, the reduction gear mechanism 30 has a rotating shaft 10 which is an input shaft, a pinion gear (first gear) 11 having a first tooth portion 11a provided on the outer periphery of the rotating shaft 10, and three planetary gears 12a, 12b, and 12c which are second gears meshing with the first tooth portion 11a. The three planetary gears 12a, 12b, and 12c each have a second tooth portion 12e which meshes with the first tooth portion 11a, and are arranged side by side at approximately equal intervals in the circumferential direction Q2 of the rotating shaft 10.

[0017] The reduction mechanism 30 also has a cylindrical accommodating section 14 that accommodates the three planetary gears 12a, 12b, and 12c, and an internal gear (third gear) 13 that is provided on the inner periphery of the accommodating section 14 and has a third tooth portion 13a that meshes with the second tooth portion 12e of the three planetary gears 12a, 12b, and 12c.

[0018] The pinion gear 11, which is the first gear, is a sun gear that rotates in the reduction gear mechanism 30. The pinion gear 11 is provided integrally with the rotating shaft 10 on the outer periphery of the rotating shaft 10, and has a first tooth portion 11a that extends in a spiral shape along the longitudinal direction Q1 of the rotating shaft 10, as shown in FIG. 5. The first tooth portion 11a has one tooth, and the pinion gear 11 is also called a one-tooth pinion gear. That is, in a cut surface in the radial direction Q3 at any position in the longitudinal direction Q1 of the rotating shaft 10, only one tooth portion (the first tooth portion 11a) is formed. Furthermore, in the tooth profile (tooth profile cross section) of the cut surface in the radial direction Q3 of the rotating shaft 10, the first tooth portion 11a has an arc-shaped portion 11b that is at least partially formed in an arc shape.

[0019] The three planetary gears 12a, 12b, and 12c that are second gears are arranged side by side in the circumferential direction Q2 of the rotating shaft 10 as shown in Fig. 4, and each has a spiral second tooth portion 12e as shown in Fig. 6. The second tooth portion 12e meshes with the first tooth portion 11a in a state where it contacts a portion where the tooth profile (tooth profile cross section) of the cut surface of the pinion gear 11 shown in Fig. 5 forms an arc shape. That is, the second tooth portion 12e of each of the three planetary gears 12a, 12b, and 12c meshes with the arc-shaped portion 11b of the first tooth portion 11a of the pinion gear 11 in a state where it contacts the arc-shaped portion 11b.

[0020] 3 and 4, the internal gear 13, which is the third gear, is provided on the inner periphery of the cylindrical housing portion 14 and has a third tooth portion 13a that meshes with the second tooth portions 12e of the planetary gears 12a, 12b, and 12c. The third tooth portion 13a is formed in a spiral shape on the inner periphery of the cylindrical housing portion 14. In the reduction mechanism 30 of this embodiment, the internal gear 13 is a fixed internal gear.

[0021] Next, the internal structure of the reduction gear mechanism 30 will be described in detail. As shown in Fig. 1 and Fig. 2, a rotating shaft 10, which is an input shaft and has a pinion gear 11 provided on its outer periphery, is rotatably supported by bearings 10b and 10c. The rotating shaft 10 rotates around a rotation center 10a. The bearings 10b and 10c are each fixed to a planetary carrier 16, and the planetary carrier 16 is rotatably attached to the rotating shaft 10 via the bearings 10b and 10c.

[0022] The planetary carrier 16 is formed in a cylindrical shape, and its outer periphery is rotatable with respect to the outer periphery frame of the reduction gear mechanism 30 via bearings 17a and 18a. That is, the planetary carrier 16 is rotatable with respect to the bearing holders 17 and 18, which are the outer periphery frame of the reduction gear mechanism 30, via the bearings 17a and 18a.

[0023] Furthermore, the fixed part 15a having the output shaft 15 is attached to the planetary carrier 16 by a pin 10d. Therefore, when the planetary carrier 16 rotates, the fixed part 15a and the output shaft 15 rotate together with the rotation of the planetary carrier 16. Similarly, when the planetary carrier 16 rotates, the fixed part 19 fixed to the planetary carrier 16 via a pin 19a rotates together with the rotation of the planetary carrier 16. In the reduction gear mechanism 30, the rotating shaft 10 and the output shaft 15 are arranged on approximately the same axis.

[0024] The three planetary gears 12a, 12b, and 12c, each having a second tooth portion 12e meshing with the first tooth portion 11a of the pinion gear 11 provided on the rotating shaft 10, are provided on three fixed shafts 12i attached to the planetary carrier 16. Specifically, each of the three fixed shafts 12i is fixed to the planetary carrier 16 and is rotatable around the rotating shaft 10. The three planetary gears 12a, 12b, and 12c are rotatably provided on the fixed shaft 12i via bearings 12j and 12k, respectively. As shown in FIG. 4, the second tooth portion 12e of each of the three planetary gears 12a, 12b, and 12c is formed to be twisted with respect to the gear shaft. That is, each of the three planetary gears 12a, 12b, and 12c is a helical gear.

[0025] In addition, since the three planetary gears 12a, 12b, and 12c are each provided rotatably about the fixed shaft 12i, the rotation center 12h of each of the three planetary gears 12a, 12b, and 12c is also the axis center of the fixed shaft 12i.

[0026] A cylindrical housing portion 14 is provided on the inner periphery of the bearing holder 17. As shown in Figs. 2 to 4, an internal gear 13 having a third tooth portion 13a meshing with the second tooth portion 12e of each of the three planetary gears 12a, 12b, and 12c is formed on the inner periphery of the housing portion 14. In the reduction gear mechanism 30 of this embodiment, the internal gear 13 is a gear that is fixed so as not to rotate. The third tooth portion 13a is formed twisted with respect to the gear shaft, and the internal gear 13 of the housing portion 14 that meshes with the three planetary gears 12a, 12b, and 12c is also a helical gear.

[0027] With the above-described structure, in the reduction gear mechanism 30 of the present embodiment, the first tooth portion 11a of the pinion gear 11 of the rotating shaft 10 meshes with the second tooth portion 12e of each of the three planetary gears 12a, 12b, and 12c, and further, the second tooth portion 12e of each of the three planetary gears 12a, 12b, and 12c meshes with the third tooth portion 13a of the internal gear 13. Therefore, when the rotating shaft 10 rotates, each of the three planetary gears 12a, 12b, and 12c rotates (rotates). At this time, the internal gear 13 meshing with the three planetary gears 12a, 12b, and 12c is a gear that does not rotate, and the three planetary gears 12a, 12b, and 12c are each rotatably provided with respect to a fixed shaft 12i that is rotatably attached around the rotating shaft 10. As a result, each of the three planetary gears 12a, 12b, and 12c revolves around the rotating shaft 10. The planetary carrier 16 rotates in conjunction with the revolutions of the three planetary gears 12a, 12b, and 12c, and the output shaft 15 fixed to the planetary carrier 16 also rotates. Therefore, when the rotating shaft 10 rotates, the output shaft 15, which is disposed on approximately the same axis as the rotating shaft 10, rotates at a reduced speed.

[0028] The second tooth portion 12e of each of the three planetary gears 12a, 12b, and 12c meshes with the first tooth portion 11a of the pinion gear 11 in a state where the tooth profile (tooth profile cross section) of the cut surface of the pinion gear 11 shown in Fig. 5 is in contact with an arc-shaped portion. That is, the second tooth portion 12e of each of the three planetary gears 12a, 12b, and 12c meshes with the arc-shaped portion 11b of the first tooth portion 11a of the pinion gear 11 in a state where the second tooth portion 12e of each of the three planetary gears 12a, 12b, and 12c abuts and meshes with the arc-shaped portion 11b of the first tooth portion 11a of the pinion gear 11. In other words, the second tooth portion 12e of each of the three planetary gears 12a, 12b, and 12c abuts and meshes with the arc-shaped portion 11b of the first tooth portion 11a of the pinion gear 11.

[0029] Here, for example, in a reduction gear mechanism including a sun gear and three planetary gears that mesh with the sun gear and revolve around the sun gear while rotating (spinning) on ​​their axes, if the sun gear and the three planetary gears are each spur gears, in order to further increase the reduction ratio, it becomes necessary to reduce the number of planetary gears from three to two. In this case, if the number of planetary gears is reduced from three to two, the strength of the reduction gear mechanism decreases to two-thirds. On the other hand, if the number of planetary gears is reduced to two to ensure the strength of the reduction gear mechanism, it becomes necessary to increase the diameter of each planetary gear. As a result, a problem occurs in that the reduction gear mechanism becomes larger in size.

[0030] However, in the reduction gear mechanism 30 of the present embodiment, the second tooth portion 12e of each of the three planetary gears 12a, 12b, and 12c is formed in a spiral shape, and the spiral second tooth portion 12e meshes with the first tooth portion 11a of the pinion gear 11, which is a sun gear. At this time, the first tooth portion 11a of the pinion gear 11 is also formed in a spiral shape. In addition, the pinion gear 11 meshes with the three planetary gears 12a, 12b, and 12c, and the three planetary gears 12a, 12b, and 12c also mesh with the internal gear 13 having the third tooth portion 13a formed in a spiral shape. This increases the meshing ratio between the gears, thereby increasing the strength of each tooth surface, and the strength of the reduction gear mechanism 30 can be ensured.

[0031] In addition, the pinion gear 11 having the first helical tooth portion 11a meshes with the three planetary gears 12a, 12b, and 12c each having a second helical tooth portion 12e, and the internal gear 13 having a third helical tooth portion 13a, and the meshing of the gears is performed continuously, so that the rotation of each gear becomes smooth. This makes it possible to suppress vibration caused by the rotation of each gear, and therefore vibration of the reduction mechanism 30.

[0032] Also, the second tooth portion 12e of each of the three planetary gears 12a, 12b, and 12c meshes with the arc-shaped portion 11b of the first tooth portion 11a of the pinion gear 11 in contact with the pinion gear 11. Furthermore, each of the three planetary gears 12a, 12b, and 12c is shaped to mesh with the pinion gear 11 at a tip circle 12g smaller than the pitch circle 12f, as shown in FIG. 6. In most cases, gears mesh with each other at a tip circle 12g larger than the pitch circle 12f, but in the case of the planetary gear 12 meshing with the pinion gear 11 having one tooth, the pitch circle 12f is larger than the tip circle 12g. As a result, in the reduction gear mechanism 30 of this embodiment, each of the three planetary gears 12a, 12b, and 12c meshes with each other at the tip circle 12g shown in FIG. 6, so that the diameters of each of the three planetary gears 12a, 12b, and 12c can be reduced. As a result, the reduction mechanism 30 can be made smaller.

[0033] That is, even if the reduction mechanism 30 has a structure including three planetary gears 12a, 12b, and 12c, the strength of the reduction mechanism 30 can be ensured without increasing the diameter of each planetary gear. In other words, the strength of the reduction mechanism 30 can be ensured while the reduction mechanism 30 is miniaturized. That is, the reduction mechanism 30 can have a large reduction ratio while being miniaturized.

[0034] Next, an explanation will be given of the arrangement conditions of the planetary gears 12 for meshing without interference between adjacent planetary gears 12 in a reduction gear mechanism 30 including a pinion gear 11 with one tooth and a plurality of planetary gears 12 meshing with the pinion gear 11. In the reduction gear mechanism 30 having the above-described structure, when the number of planetary gears 12 is three or more, it is necessary to avoid interference between the planetary gears 12 and adjacent planetary gears 12, and since this also affects the strength of the reduction gear mechanism 30, it is necessary to decide how many planetary gears 12 to set and design in the early stages of designing the reduction gear mechanism 30.

[0035] First, a description will be given of interference of a planetary gear using a general involute gear 40 shown in Fig. 9. Equation (A) for determining the presence or absence of interference in the case of a general involute gear 40 is given as follows.

[0036] 2+Zb<(Za+Zb)×sin(180° / N)...Equation (A). Here, Za is the number of teeth of the sun gear, Zb is the number of teeth of the planetary gear 12, and N is the number of planetary gears. In equation (A), the value of sin is a variable that takes a value between 1 and -1. Note that the value of sin in equation (A) is not a function that increases the value on the right side, so the number N of planetary gears is ignored and the value of sin is assumed to be 1, which is the maximum value. In this case, if the sun gear is a pinion gear 11 with one tooth, Za=1, so equation (A) becomes (2+Zb)<(1+Zb). In this equation (2+Zb)<(1+Zb), the value on the right side is lower than the value on the left side for all values, and this inequality does not hold. The above formula (A) is only valid when the number of teeth Za of the sun gear is three or more, and is not applicable when the sun gear is a pinion gear 11 with one tooth, as in the reduction gear mechanism 30 of this embodiment. Therefore, it is necessary to devise conditions that are applicable when the sun gear is a pinion gear 11 with one tooth.

[0037] First, we will consider the conditions for avoiding interference between adjacent planetary gears when three planetary gears 12 are provided in a reduction mechanism 30 in which the sun gear is a pinion gear 11 with one tooth. The tip circle 12g of the planetary gear 12 is determined by the specifications of the pinion gear 11 with one tooth, and is characterized by having a smaller diameter than the pitch circle 12f of the planetary gear 12. When the specifications of the pinion gear 11 with one tooth have not been determined, the pitch circle 12f of the planetary gear 12 will be considered as a condition for avoiding interference instead of the tip circle 12g of the planetary gear 12.

[0038] If the radius of pitch circle 12f of planetary gear 12 is R1 as shown in Figure 6, interference avoidance limit lines S1, S2, and S3 are set as shown in Figure 7, and the distance (center-to-center distance) between the center (rotation center 10a) of pitch circle 11c of pinion gear 11 with one tooth and the center (rotation center 12h) of pitch circle 12f of planetary gear 12 is L1, then when the sun gear is pinion gear 11 with one tooth, the following equation (B) holds.

[0039] Pitch circle radius R1 of planetary gear 12 < (center distance L1 × cosθ) Equation (B) 9, the planetary gear 12 is considered to have a tip circle 40b larger than the pitch circle 40a of the involute gear 40. In other words, if the tip circle radius of the involute gear 40 is R2 and the distance (center-to-center distance) between the center (rotation center 10a) of the pitch circle 11c of the pinion gear 11 with one tooth and the center (rotation center 40c) of the tip circle 40b of the involute gear 40 is L1, the following formula (C) is established.

[0040] Tip radius R2 of involute gear 40<(center distance L1×cosθ) Equation (C) In this case, the angle θ can be calculated by the following formula (D).

[0041] θ = (180° (sum of the interior angles of the triangle) - 90°) - (360° ÷ number of planetary gears ÷ 2) Equation (D) In other words, in the reduction mechanism 30 of this embodiment, by setting the pitch circle radius R1 of the planetary gears 12<(center-to-center distance L1×cosθ), it is possible to avoid interference between adjacent planetary gears when three planetary gears 12 are provided.

[0042] Next, a description will be given of conditions for avoiding interference between adjacent planetary gears when four planetary gears 12 are provided in a reduction mechanism 30 in which the sun gear is a pinion gear 11 with one tooth. That is, the case is one in which four planetary gears 12a, 12b, 12c, and 12d that mesh with the pinion gear 11 with one tooth are provided.

[0043] First, interference avoidance limit lines T1, T2, T3, and T4 are set as shown in Fig. 8. Furthermore, if the radius of the pitch circle 12f of the planetary gear 12 shown in Fig. 6 is R1 and the distance (center-to-center distance) between the center (rotation center 10a) of the pitch circle 11c of the pinion gear 11 with one tooth and the center (rotation center 12h) of the pitch circle 12f of the planetary gear 12 is L1, when the sun gear is the pinion gear 11 with one tooth, the following formula (B) holds, just like when three planetary gears 12 are provided.

[0044] Pitch circle radius R1 of planetary gear 12 < (center distance L1 × cosθ) Equation (B) In this case, the angle θ can be calculated by the following formula (D), similarly to the case where three planetary gears 12 are provided.

[0045] θ = (180° (sum of the interior angles of the triangle) - 90°) - (360° ÷ number of planetary gears ÷ 2) Equation (D) In other words, in the reduction mechanism 30 of this embodiment, even when four planetary gears 12 are provided, interference between adjacent planetary gears can be avoided by setting the relationship of pitch circle radius R1<(center distance L1×cos θ) of the planetary gears 12.

[0046] Next, an application example of the speed reduction mechanism 30 of this embodiment will be described.

[0047] The reduction mechanism 30 can be applied to an industrial robot 35 as shown in FIG. 10. The robot 35 includes, for example, a body 35a, a shoulder 35b attached to the body 35a, an elbow 35c connected to the shoulder 35b, and a wrist 35d connected to the elbow 35c. A motor unit 34 provided with a reduction mechanism 30 as shown in FIG. 11 is incorporated in each of the above-mentioned parts. Each motor unit 34 includes a motor 31, the reduction mechanism 30 of this embodiment, an encoder 32, and a driver board 33. The rotating shaft 10 of the motor 31 is the input shaft of the reduction mechanism 30, and the rotating shaft 10 is rotated by the driving of the motor 31, and the output shaft 15 (see FIG. 1) reduced in speed by the reduction mechanism 30 is rotated.

[0048] By incorporating the motor unit 34 equipped with the reduction mechanism 30 of this embodiment into various parts of the robot 35, it is possible to reduce the size of the reduction mechanism 30, and therefore the robot 35 can be made more compact.

[0049] According to the reduction gear mechanism 30 of this embodiment, the reduction gear mechanism 30 can be made smaller, so that the load on the motor 31 that operates the reduction gear mechanism 30 can be reduced. As a result, the motor unit 34 including the reduction gear mechanism 30 can be operated efficiently. This makes it possible to contribute to the Sustainable Development Goals (SDGs) led by the United Nations, particularly to Goal 7 (Ensure access to affordable, reliable, sustainable and modern energy) and Goal 13 (Take urgent action to combat climate change and its impacts).

[0050] The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the gist of the present invention. For example, in the above-described embodiment, the speed reduction mechanism 30 is applied to the motor unit 34 incorporated in each portion of the robot 35, but the speed reduction mechanism can also be applied to a motor unit equipped with a drive source for a wiper device mounted on a vehicle, or other drive sources such as a power window device or a sunroof device. [Explanation of symbols]

[0051] 10: rotating shaft, 10a: center of rotation, 10b, 10c: bearings, 10d: pin, 11: pinion gear (first gear), 11a: first tooth portion, 11b: arc-shaped portion, 11c: pitch circle, 12, 12a, 12b, 12c, 12d: planetary gear (second gear), 12e: second tooth portion, 12f: pitch circle, 12g: tip circle, 12h: center of rotation, 12i: fixed shaft, 12j, 12k: bearings, 13: internal gear (third gear), 13a: third tooth portion, 14: housing portion, 15: output shaft, 15a: fixed portion, 16: planetary carrier, 17: bearing holding portion, 17a: Bearing, 18: bearing holder, 18a: bearing, 19: fixed part, 19a: pin, 30: reduction mechanism, 31: motor, 32: encoder, 33: driver board, 34: motor unit, 35: robot, 35a: body, 35b: shoulder, 35c: elbow, 35d: wrist, 40: involute gear, 40a: pitch circle, 40b: tip circle, L1: center distance, Q1: longitudinal direction, Q2: circumferential direction, Q3: radial direction, R1: pitch circle radius, R2: tip circle radius, S1, S2, S3, T1, T2, T3, T4: interference avoidance limit line, θ: angle

Claims

1. A rotation axis; a first gear provided on an outer periphery of the rotating shaft and including a first tooth portion extending helically along a longitudinal direction of the rotating shaft; a plurality of second gears each including a spiral second tooth portion meshing with the first tooth portion and arranged side by side in a circumferential direction of the rotating shaft; a housing portion that houses the plurality of second gears; a third gear provided on an inner periphery of the housing portion and including a spiral third tooth portion that meshes with the second tooth portion; having At least a part of the first tooth portion has a tooth cross section formed in an arc shape, The second tooth portion meshes with the first tooth portion in a state of contact with a portion of the tooth profile cross section that is arc-shaped.

2. 2. The reduction mechanism according to claim 1, A reduction mechanism, wherein at least three of the second gears are arranged side by side in the circumferential direction of the rotation shaft.

3. The reduction mechanism according to claim 1 or 2, The pitch circle radius of the second gear is R1, a center distance from the rotation center of the rotation shaft to the rotation center of the second gear is L1, If the angle calculated by the formula (180° (sum of the interior angles of the triangle) - 90°) - (360° ÷ number of the second gears ÷ 2) is θ, A reduction mechanism in which the pitch circle radius R1 is smaller than (the center-to-center distance L1 × cos θ).

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