TW201908620A - Wave gear device - Google Patents

Abstract

This wave gear device is provided with: a non-circular cam which rotates about the center axis; a flexible ball bearing which is mounted on the outer circumferential surface of the non-circular cam and which has a radial length variable in the circumferential direction according to rotation of the non-circular cam; a flexible externally toothed gear which has a cylindrical shape extending in the axial direction, of which the lower end in the axial direction has an inner circumferential surface in contact with the outer circumferential surface of the ball bearing, and which has a plurality of external teeth provided at a certain pitch in the circumferential direction on the outer circumferential surface of the lower end in the axial direction; and an internally toothed gear that is disposed radially outside the flexible externally toothed gear, that includes inner teeth the number of which is different from the number of the plurality of external teeth, and that partially meshes with the flexible externally toothed gear. The outer circumferential surface of the ball bearing and the inner circumferential surface of the lower end of the flexible externally toothed gear are in surface contact with each other. A space is provided, in the contact portion, at a position facing, in the radial direction, a ball in the ball bearing.

Description

Wave gear device

The present invention relates to a wave gear device.

Japanese Patent No. 5734102 discloses a wave gear device that decelerates input rotation and transmits it to the load side. The wave gear device described in this publication includes an annular rigid internal gear, a flexible external gear disposed inside the rigid internal gear, and a wave generator embedded inside the flexible external gear. The flexible external gear is bent in the radial direction by the wave generator and partially engaged with the internal gear. Moreover, the input rotation is decelerated by the relative rotation corresponding to the difference in the number of teeth of the two gears. [Patent Document 1] Japanese Patent No. 5734102

[Problems to be Solved by the Invention] In the wave gear device of Japanese Patent No. 5734102, a radial bending is generated in the wave generator, whereby a stress toward the radially outer side is generated in the wave bearing of the wave generator. Thereby, the flexible external gear is pressed radially outward by the balls of the wave bearing. Moreover, a high stress is applied to the portion of the flexible externally toothed wheel that is pressed by the ball, and there is a flaw in destroying the flexible externally toothed gear.

In view of such a problem, an object of the present invention is to provide a wave gear device that reduces the load applied from a bearing to a flexible externally toothed gear.

[Means for Solving the Problems] In order to solve the above problems, the present invention is a wave gear device comprising: a non-true circular cam that rotates around a central axis extending from above; a flexible ball bearing is attached to the non-circular The outer peripheral surface of the true circular cam has a radial length that varies in the circumferential direction corresponding to the rotation of the non-true circular cam; the flexible externally toothed gear has a cylindrical shape elongated in the axial direction and an axial direction An inner circumferential surface of the side end portion contacts an outer circumferential surface of the ball bearing, a plurality of outer teeth are circumferentially disposed on an outer circumferential surface of the lower end portion at a fixed pitch; and an internal gear is disposed in the a radially outer side of the flexible externally toothed gear, having internal teeth different in number of teeth from the plurality of external teeth, and partially engaging with the flexible externally toothed gear; an outer circumferential surface of the ball bearing and the The inner peripheral surface of the lower end portion of the flexible externally toothed gear is in surface contact; and the inner peripheral surface of the lower end portion of the flexible externally toothed gear as the outer peripheral surface of the ball bearing Contact portion and radial direction with the ball bearing The position of the ball on the provided space.

[Effects of the Invention] According to the present invention, the radial length of the ball bearing is changed by the non-true circular cam. In this variation, when the length of the radial direction becomes long, the outer peripheral surface of the ball bearing is pressed radially outward by the balls of the ball bearing and bent. The bent portion enters into a space provided between the ball bearing and the flexible externally toothed gear. Therefore, stress from the ball bearing is difficult to be transmitted to the flexible externally toothed gear. As a result, the load from the ball bearing to the flexible externally toothed gear is reduced, and damage to the flexible externally toothed gear can be suppressed.

Hereinafter, an exemplary embodiment of the present application will be described with reference to the drawings. In the present application, the direction parallel to the central axis of the wave gear device is referred to as "axis direction", and the direction orthogonal to the central axis of the wave gear device is referred to as "radial direction". The direction of the arc of the center axis of the wave gear device is referred to as "circumferential direction". In the present application, the axial direction is referred to as the vertical direction, and the rotation output portion side is set upward with respect to the rotation input portion, and the shape or positional relationship of each portion will be described. However, there is no intention to define the direction in use of the wave gear device of the present application by the definition of the up and down direction.

In addition, in the present application, the "parallel direction" also includes a substantially parallel direction. In addition, in the present application, the "orthogonal direction" also includes directions that are substantially orthogonal.

<1. Embodiment 1> <1.1. Configuration of Wave Gear Device> FIG. 1 is a cross-sectional view of a wave gear device 100 according to an exemplary embodiment of the present application. Fig. 2 is a cross-sectional view taken along line II-II of Fig. 1.

The wave gear device 100 includes a wave generator 4 that rotates around the center axis 9 . The wave generator 4 has a non-true circular cam 41 and a ball bearing 42.

A rotation input unit (not shown) is connected to the non-true round cam 41. The rotation input unit transmits a rotational force from the motor, for example, and rotates in the circumferential direction around the central axis 9. The non-true circular cam 41 transmits rotation from the rotation input unit, and rotates around the central axis 9 together with the rotation input unit. The non-true circular cam 41 is elliptical when viewed from the axial direction.

The ball bearing 42 is disposed on the outer side in the radial direction of the non-true round cam 41 and is attached to the outer peripheral surface of the non-true round cam 41. The ball bearing 42 has flexibility, and when attached to the non-true round cam 41, it is curved in an elliptical shape along the outer peripheral surface of the non-true circular cam 41 as viewed in the axial direction.

The wave gear device 100 includes an internal gear 3 . The internal gear 3 is a cylindrical shape surrounding the central axis 9, and is a true circular shape when viewed from the axial direction. The internal gear 3 is disposed radially outward of the ball bearing 42. Further, the internal gear 3 is, for example, non-rotatably fixed to a cover or the like (not shown) of the wave gear device 100. A plurality of internal teeth 31 are provided on the inner circumferential surface of the internal gear 3 in a circumferential direction at a fixed pitch.

The wave gear device 100 includes a flexible externally toothed gear 5. The flexible externally toothed gear 5 is a cylindrical member that surrounds the center shaft 9 and is elongated in the axial direction. The lower end portion 50 of the flexible externally toothed gear 5 in the axial direction is disposed between the ball bearing 42 and the internal gear 3 . The inner circumferential surface of the lower end portion 50 is in contact with the outer circumferential surface of the ball bearing 42. A plurality of external teeth 501 having a different number of teeth than the plurality of internal teeth 31 of the internal gear 3 are provided on the outer circumferential surface of the lower end portion 50 in the circumferential direction at a fixed pitch.

The lower end portion 50 of the flexible externally toothed gear 5 is attached to the ball bearing 42. The ball bearing 42 is bent into an elliptical shape as described above. Therefore, the lower end portion 50 of the flexible externally toothed gear 5 attached to the ball bearing 42 is also curved in an elliptical shape. The short axis of the lower end portion 50 bent into an elliptical shape is shorter than the inner diameter of the true circular internal tooth gear 3. Further, the long axis of the lower end portion 50 is substantially the same as the inner diameter of the internal gear 3 . Therefore, in the long-axis portion of the lower end portion 50, the external teeth 501 of the flexible externally toothed gear 5 mesh with the internal teeth 31 of the internal gear 3.

When the non-true round cam 41 rotates, the length of the flexible externally toothed gear 5 in the radial direction is displaced in the circumferential direction. Thereby, the meshing position of the flexible externally toothed gear 5 and the internal gear 3 moves in the circumferential direction. In addition, the internal gear 3 is non-rotatably fixed. As a result, when the flexible externally toothed gear 5 having different numbers of teeth rotates relative to the internal gear 3, the flexible externally toothed gear 5 rotates at a smaller number of revolutions than the non-true circular cam 41.

The upper end portion of the flexible externally toothed gear 5 in the axial direction expands inward in the radial direction. Although not shown, the wave gear device 100 includes an output shaft that is rotatable about the center axis 9 and connected to the load. The upper end portion of the flexible externally toothed gear 5 in the axial direction is fixed to the output shaft. Thereby, when the flexible externally toothed gear 5 rotates around the central axis 9, the output shaft also rotates. Moreover, the rotation is transmitted toward the load. As described above, the flexible externally toothed gear 5 rotates at a smaller number of revolutions than the non-true round cam 41. In other words, the output shaft that rotates together with the flexible externally toothed gear 5 also rotates at a smaller number of revolutions than the non-true circular cam 41. As described above, the rotation input from the motor (not shown) to the non-true round cam 41 is decelerated, and is output to the load via the output shaft.

<1.2. Stress on Ball Bearing 42> The ball bearing 42 is curved in an elliptical shape due to the non-true round cam 41. At this time, in the portion which becomes the long axis of the ball bearing 42, a stress toward the outside in the radial direction is generated. Further, the outer circumferential surface of the ball bearing 42 (the outer circumferential surface of the outer ring) is pressed outward in the radial direction by the balls, and the pressed portion is bent. As before, if the curved portion of the outer peripheral surface of the ball bearing 42 abuts against the inner peripheral surface of the flexible externally toothed gear 5, there is a possibility that a high point due to point contact occurs in the flexible externally toothed gear 5. The stress causes the flexible externally toothed gear 5 to be damaged. Therefore, in the present embodiment, the flexible externally toothed gear 5 has a configuration in which it is difficult to transmit the stress from the ball bearing 42.

3 is an enlarged view of a contact portion of the flexible externally toothed gear 5 and the internal gear 3 .

The inner peripheral surface of the lower end portion 50 of the flexible externally toothed gear 5 is in contact with the outer peripheral surface of the ball bearing 42. A concave portion 51 that is recessed outward in the radial direction is provided on the inner peripheral surface of the lower end portion 50. As shown in FIG. 2, the concave portion 51 is provided at a position facing the ball center point of the ball bearing 42 in the radial direction along the circumferential direction. The length of the recess 51 in the axial direction is 20% to 120% of the diameter of the ball of the ball bearing 42. However, it is more preferable that the length of the concave portion 51 in the axial direction is 80% to 100% of the diameter of the ball of the ball bearing 42. A space 55 is provided between the inner circumferential surface of the lower end portion 50 and the outer circumferential surface of the ball bearing 42 by the concave portion 51.

As described above, the outer circumferential surface of the ball bearing 42 is curved outward in the radial direction due to the pressing from the balls. Moreover, the curved portion of the outer peripheral surface of the ball bearing 42 enters the space 55. Therefore, the vicinity of the apex of the curved portion in the radial direction does not abut against the inner peripheral surface of the flexible externally toothed gear 5. Thereby, the load from the ball bearing 42 to the flexible externally toothed gear 5 is reduced, and damage of the flexible externally toothed gear 5 can be suppressed.

<2. Second embodiment> The second embodiment will be described below. The configuration of the second embodiment is different from the first embodiment in that the stress from the ball bearing 42 to the flexible externally toothed gear 5 is hard to be transmitted.

4 is an enlarged view of a contact portion of the flexible externally toothed gear 5 and the internal gear 3 .

In this example, a concave portion 43 that is recessed inward in the radial direction is provided at a central portion in the axial direction of the outer circumferential surface of the ball bearing 42. The recessed portion 43 is provided at a position opposed to the center point of the ball of the ball bearing 42 in the radial direction. Further, similarly to the concave portion 51 of the first embodiment, the concave portion 43 is provided along the circumferential direction. The length of the recessed portion 43 in the axial direction is 20% to 120% of the diameter of the ball of the ball bearing 42. However, it is more preferable that the length of the concave portion 51 in the axial direction is 80% to 100% of the diameter of the ball of the ball bearing 42. A space 45 is provided between the outer circumferential surface of the ball bearing 42 and the inner circumferential surface of the lower end portion 50 of the flexible externally toothed gear 5 by the concave portion 43.

In the same manner as in the first embodiment, when the outer circumferential surface of the ball bearing 42 is bent outward in the radial direction by the pressing of the balls, the curved portion generated on the surface of the concave portion 43 enters the space 45. Therefore, the vicinity of the apex of the curved portion in the radial direction does not abut against the inner peripheral surface of the flexible externally toothed gear 5. Thereby, the load from the ball bearing 42 to the flexible externally toothed gear 5 is reduced, and damage of the flexible externally toothed gear 5 can be suppressed.

<3. Modifications> Although the exemplary embodiments of the present invention have been described above, the present invention is not limited to the embodiments.

Fig. 5 is a cross-sectional view showing a wave gear device 100A of another example. The upper end portion of the flexible externally toothed gear 5A provided in the wave gear device 100A in the axial direction expands outward in the radial direction. In the case of this configuration, the output shaft connected to the load can be disposed radially outward of the case of FIG. 1 .

In the first embodiment and the second embodiment, the length of the space 45 and the space 55 in the axial direction is set to 20% to 120% of the diameter of the ball of the ball bearing 42, and more preferably 80% to 100%. It is not limited to this. Further, the length (depth) of the radial direction of the space 45 and the space 55 can be appropriately changed in accordance with the degree of bending of the outer peripheral surface of the ball bearing 42. In addition, a recess may be provided in both the inner circumferential surface of the flexible externally toothed gear 5 and the outer circumferential surface of the ball bearing 42 to provide a space.

In addition, the shape of the minute portion of the wave gear device 100 may be different from the shape shown in each drawing of the present application. Further, each element appearing in the above-described embodiment or modification may be appropriately combined within a range in which no contradiction occurs.

[Industrial Applicability] This application can be applied to a wave gear device.

3‧‧‧ internal gear

4‧‧‧ fluctuation generator

5‧‧‧Flexible external gear

5A‧‧‧Flexible external gear

9‧‧‧ center axis

31‧‧‧ internal teeth

41‧‧‧Non-circular cam

42‧‧‧Ball bearings

43‧‧‧ recess

45‧‧‧ Space

50‧‧‧lower end

51‧‧‧ recess

55‧‧‧ Space

100‧‧‧ Wave gear device

100A‧‧‧ Wave gear device

501‧‧‧ external teeth

Fig. 1 is a cross-sectional view showing a wave gear device of an exemplary embodiment of the present application. Fig. 2 is a cross-sectional view taken along line II-II of Fig. 1. Fig. 3 is an enlarged view of a contact portion of a flexible externally toothed gear and an internally toothed gear. 4 is an enlarged view of a contact portion of a flexible externally toothed gear and an internally toothed gear. Fig. 5 is a cross-sectional view showing a wave gear device of another example.

Claims (8)

A wave gear device, comprising: a non-true circular cam rotating around a central shaft extending upward; a flexible ball bearing mounted on an outer circumferential surface of the non-true circular cam, radial The length changes in the circumferential direction in accordance with the rotation of the non-true circular cam; the flexible externally toothed gear has a cylindrical shape elongated in the axial direction, and an inner peripheral surface of the lower end portion in the axial direction contacts the ball a peripheral surface of the bearing, a plurality of external teeth are disposed on the outer peripheral surface of the lower end portion at a fixed pitch in a circumferential direction; and an internal gear is disposed radially outward of the flexible externally toothed gear, An internal tooth having a different number of teeth than the plurality of external teeth, and partially engaging with the flexible externally toothed gear; an outer peripheral surface of the ball bearing and the lower end of the flexible externally toothed gear The inner peripheral surface of the portion is in surface contact with the ball in the radial direction as a contact portion between the outer peripheral surface of the ball bearing and the inner peripheral surface of the lower end portion of the flexible externally toothed gear. The position of the ball opposite to the bearing is set Room. The wave gear device according to claim 1, wherein a central portion of the inner circumferential surface of the lower end portion of the flexible externally toothed gear in the axial direction is recessed outward in the radial direction. The wave gear device according to the first or second aspect of the invention, wherein the central portion of the outer circumferential surface of the ball bearing in the axial direction is recessed toward the inner side in the radial direction. The wave gear device according to any one of claims 1 to 3, wherein the space is disposed at a position radially opposed to a ball center point of the ball bearing. The wave gear device according to claim 4, wherein the length of the space in the axial direction is 20% to 120% of the diameter of the ball of the ball bearing. The wave gear device according to claim 5, wherein the length of the space in the axial direction is 80% to 100% of the diameter of the ball of the ball bearing. The wave gear device according to any one of the first to sixth aspect, wherein the upper end portion of the flexible externally toothed gear in the axial direction extends radially inward. The wave gear device according to any one of claims 1 to 6, wherein the upper end portion of the flexible externally toothed gear in the axial direction extends outward in the radial direction.