JP2021173308A - Wave motion gear device - Google Patents

Abstract

To provide a wave motion gear device capable of suppressing abrasion wear by dispersing a load to a bearing, even when an external gear is deformed.SOLUTION: A wave motion gear device 100 includes: an internal gear 110 having a plurality of inner teeth 111 on an inner peripheral surface; a flexible external gear 120 having a plurality of outer teeth 121 on an outer peripheral surface; and a wave motion generator 130 for elliptically deflecting the external gear 120 to engage the outer teeth 121 of a long-diameter part with the inner teeth 111 of the internal gear 110, and moving the engagement position in a circumferential direction. The wave motion generator 130 includes an elliptic cam 136, and a flexible bearing 131 disposed on an outer peripheral surface of the elliptic cam 136. One of an inner peripheral surface of the external gear 120 and an outer peripheral surface of the flexible bearing 131 has a concave surface portion 128 formed into the shape of a concave surface. The other of the inner peripheral surface of the external gear 120 and the outer peripheral surface of the flexible bearing 131 has a convex surface portion 139 formed into the shape of a convex surface. The convex surface portion 139 and the concave surface portion 128 are kept into contact with each other at two positions with a prescribed interval in an axial direction.SELECTED DRAWING: Figure 2

Description

The present invention relates to a strain wave gearing.

Conventionally, there is a wave gearing device as one of the gearing devices used as a speed reducer. This wave gear device has a cylindrical internal gear made of a rigid body, an external gear that has external teeth that mesh with the internal teeth of the internal gear, and has a flexible tubular external gear, and internal teeth and external teeth. Is provided with an elliptical wave generator that meshes at a predetermined position and orbits the meshing position along the internal gear (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 11-351341

By the way, in such a wave gear device, the external gear is deformed in a tapered shape by the bearing which is a part of the wave generator. Due to this deformation, the contact area with respect to the bearing becomes small on the outer peripheral surface of the external gear. As a result, the load is concentrated on the bearing, and there is a possibility that wear may occur between the external gear and the bearing.

An object of the present invention is to provide a strain wave gearing capable of distributing a load on a bearing and suppressing wear even if the external gear is deformed.

In order to achieve the above object, the wave gear device according to the present disclosure has a cylindrical internal gear having a plurality of internal teeth on the inner peripheral surface and a cylindrical flexibility having a plurality of external teeth on the outer peripheral surface. The external gear and the external gear are placed inside the external gear, and the external gear is bent in an elliptical shape to mesh the external teeth of the long diameter part with the internal teeth of the internal gear to move the meshing position in the circumferential direction. It is equipped with a wave generator to make it. The wave generator includes an elliptical cam and a flexible bearing arranged on the outer peripheral surface of the elliptical cam. One of the inner peripheral surface of the external gear and the outer peripheral surface of the flexible bearing has a concave curved surface portion formed in a concave curved surface shape. The other side of the inner peripheral surface of the external gear and the outer peripheral surface of the flexible bearing has a convex curved surface portion formed in a convex curved surface shape. The convex curved surface portion and the concave curved surface portion are in contact with each other at two points at predetermined intervals in the axial direction.

According to the wave gear device according to the present invention, even if the external gear is deformed, the load on the bearing can be dispersed and wear can be suppressed.

It is sectional drawing of the wave gear device which concerns on embodiment. It is sectional drawing which shows the part of the wave gear device which concerns on embodiment in an enlarged manner. It is sectional drawing which looked at the cross section including the line III-III in FIG. It is sectional drawing which enlarges and shows a part of the body part in the external tooth gear which concerns on embodiment. It is sectional drawing which shows the concave curved surface part and convex curved surface part which concerns on modification 1. FIG. It is sectional drawing which shows the part of the wave gear device which concerns on modification 2 in an enlarged manner.

Hereinafter, embodiments of the strain wave gearing according to the present invention will be described with reference to the drawings. It should be noted that all of the embodiments described below show comprehensive or specific examples. Numerical values, shapes, materials, components, arrangement positions of components, connection forms, and the like shown in the following embodiments are examples, and are not intended to limit the present invention. Further, among the components in the following embodiments, the components not described in the independent claims indicating the embodiment according to the embodiment of the present disclosure will be described as arbitrary components. The embodiment of the present disclosure is not limited to the current independent claims, but may be expressed by other independent claims.

In addition, the drawings are schematic views in which emphasis, omission, and ratio are adjusted as appropriate to show the present invention, and may differ from the actual shape, positional relationship, and ratio.

In the following description and drawings, the axial direction of the wave gear device 100 is defined as the Z-axis direction, and the two directions orthogonal to each other on the plane orthogonal to the Z-axis direction are defined as the X-axis direction and the Y-axis direction. Define. In the following description, for example, the positive side in the Z-axis direction indicates the arrow direction side of the Z-axis, and the negative side in the Z-axis direction indicates the side opposite to the positive side in the Z-axis direction. The same applies to the X-axis direction and the Y-axis direction.

[Structure of strain wave gearing]
FIG. 1 is a cross-sectional view of a strain wave gearing according to an embodiment. FIG. 2 is an enlarged cross-sectional view showing a part of the strain wave gearing according to the embodiment. FIG. 3 is a cross-sectional view of the cross section including lines III-III in FIG. As shown in these figures, the wave gear device 100 includes an internal gear 110, an external gear 120, and a wave generator 130.

The internal gear 110 is a metal member having a structurally higher rigidity than the external gear 120 and having an inner peripheral surface of a cylinder, and is a member that is separated from the rotation of the input shaft body and the output shaft body and attached in a fixed state. be. The internal gear 110 has a plurality of internal teeth 111 (see FIG. 2) formed on the inner peripheral surface. A plurality of through holes 112 arranged at predetermined intervals in the circumferential direction are formed on the outer peripheral portion of the internal gear 110. For example, a screw (not shown) is inserted into the plurality of through holes 112, and the wave gear device 100 is screwed to a fixing object to be fixed.

The external gear 120 is formed in a cup shape. Therefore, the wave gear device 100 may be referred to as a cup-type wave gear device. Specifically, the external gear 120 is a cylindrical metal member having lower rigidity and flexibility than the internal gear 110. The external gear 120 is a member having a plurality of external teeth 121 (see FIG. 2) that mesh with the internal teeth 111 of the internal gear 110 on the outer peripheral surface of one end (the end on the negative side in the Z-axis direction in the drawing). be. The external gear 120 includes a flange portion 122 and a boss portion 123. Here, "one end" means the input shaft body side (minus side in the Z-axis direction in the figure) with respect to the wave gear device 100 in the axial direction (Z-axis direction in the figure) of the external gear 120 or the wave generator 130. It is described as meaning the end of. For example, in the external gear 120, the external teeth 121 are arranged at one end. Further, "the other end", which is a synonym for "one end", means the output shaft body side (in the figure) with respect to the wave gear device 100 in the axial direction (Z-axis direction in the figure) of the external gear 120 or the wave generator 130. , Z-axis direction plus side), for example, in the external gear 120, the flange portion 122 is arranged at the other end. The "part" of the "one end" and "the other end" means a region near the end including the end.

In the external gear 120, when there is no load, specifically, when the external gear 120 is taken out from the strain wave gearing device 100 and no force is applied from the other, one end is opened and the flange portion 122 is arranged at the other end. It has a substantially bottomed cylindrical shape. The cylindrical portion of the external tooth gear 120 integrally includes a body portion 124 on which the external teeth 121 are arranged and an annular rim portion 125 extending from the body portion 124 toward the other end.

A concave curved surface portion 128 formed in a concave curved surface shape is provided on the inner peripheral surface of the body portion 124. Specifically, a concave curved surface portion 128 is provided on the inner peripheral surface of the body portion 124 at a portion corresponding to the flexible bearing 131 of the wave generator 130. The concave curved surface portion 128 is a groove portion continuous over the entire circumference of the body portion 124. The concave curved surface portion 128 is a smooth concave curved surface as a whole. When there is no load, the radius of curvature of the concave curved surface portion 128 as a whole in FIG. 2 is constant.

Further, the flatness ratio, which is the ratio of the width W1 of the external gear 120 to the tooth tip circle diameter D1 of the external gear 120 when no load is applied, is 0.25 or less. Here, the width W1 of the external gear 120 is the distance from one end of the external gear 120 to the other end (the other end of the boss 123 in the present embodiment). Due to such a flatness, the entire wave gear device 100 can be made thinner, and a compact reduction gear in which the input shaft body (not shown) and the output shaft body (not shown) are coaxially close to each other can be obtained. It can be realized. The tooth tip circle diameter D1 and width W1 of the external gear 120 are shown in FIG. 1, but in reality, the external gear 120 is taken out from the strain wave gearing device 100 and no force is applied from others. The dimensions in are adopted. The flatness is preferably 0.15 or more. If the flatness is less than 0.15, the desired transmission efficiency cannot be achieved. Further, the flatness is preferably 0.2 or more and 0.25 or less. According to this, along with the miniaturization of the strain wave gearing 100, it becomes easy to realize a desired torque capacity.

The flange portion 122 extends inward in the radial direction from the other end of the cylindrical portion of the external gear 120, and corresponds to the bottom of the external gear 120 that transmits rotation to the output shaft. The shape of the flange portion 122 is not particularly limited, but in the case of the present embodiment, the flange portion 122 has a thin plate-like ring shape, and the diameter of the outer circumference corresponds to the diameter of the rim portion 125. , It extends integrally from the other end edge of the rim portion 125. The flange portion 122 is arranged in a plane that virtually includes the other end of the rim portion 125. In other words, the flange portion 122 is arranged flush with or substantially flush with the other end of the rim portion 125. Here, substantially flush with each other means that at least one of the other end of the rim portion 125, the flange portion 122, and the boss portion 123 is displaced in the axial direction as the external tooth gear 120 is deformed by pressing the wave generator 130. It is described as a meaning that includes an error of about the amount. That is, in order to prevent the output shaft body connected to the boss portion 123, other members such as bearings supporting the output shaft body, the other end of the rim portion 125, and the flange portion 122 from interfering with each other due to deformation of the external gear 120. Even if the flange portion 122 is provided with a dent, a protrusion, or the like within the range of the relief amount provided in the above range, the flange portion 122 is included in a substantially flush state within the range.

The wall thicknesses of the flange portion 122, the rim portion 125, and the body portion 124 are not particularly limited, and are determined by the characteristics of the materials constituting the external gear 120 and the like. In the present embodiment, the wall thicknesses of the flange portion 122 and the rim portion 125 are the same, and are thinner than the total tooth depth of the external teeth 121. Specifically, for example, when the tooth tip circle diameter D1 is 68.8 mm, the wall thickness of the flange portion 122 and the rim portion 125 is 0.5 mm or less and 0.2 mm or more. If the wall thickness of the flange portion 122 and the rim portion 125 is thicker than 0.5 mm, the deformation of the body portion 124 by the wave generator 130 is hindered and the desired transmission efficiency cannot be obtained. If the wall thickness of the flange portion 122 and the rim portion 125 is less than 0.1 mm, the desired torque capacity cannot be achieved.

The boss portion 123 is provided on the flange portion 122 in a state of projecting from the flange portion 122 to one end side, and is a portion connected to the output shaft body. The shape of the boss portion 123 is not particularly limited, but in the case of the present embodiment, the boss portion 123 has a plate-like ring shape thicker than the flange portion 122, and the outer periphery thereof is the flange portion 122. It is continuously connected to the outer circumference of. The surface portion on the other end side of the boss portion 123 is arranged flush with or substantially flush with the surface portion on the other end side of the flange portion 122. In the case of the present embodiment, the boss portion 123 slightly protrudes to the other end side from the flange portion 122. The protruding length of the boss portion 123 toward the other end is a length for avoiding interference with an output shaft body or the like attached to the boss portion 123, and the surface portion on the other end side of the boss portion 123 is a flange. It can be considered to be substantially flush with the surface portion on the other end side of the portion 122.

In the case of the present embodiment, a plurality of through holes 126 are formed in the boss portion 123 at predetermined intervals in the circumferential direction. A bolt 200 for fastening the output shaft body is inserted through each through hole 126.

The wall thickness of the boss portion 123, that is, the amount of protrusion of the boss portion 123 from the flange portion 122 to one end side is not particularly limited, and is determined by the mounting mode with the output shaft body and the like. In the present embodiment, the boss portion 123 has a structure in which a bolt is pierced through a through hole 126 provided in the boss portion 123 from one end side and the boss portion 123 and the output shaft body are fastened using the bolt. , A wall thickness (protrusion amount) is adopted so that the bolt head does not interfere with the wave generator 130 or the like.

As described above, the flatness of the entire external gear 120 is reduced by arranging the boss portion 123 to protrude from the flange portion 122 to one end side and not to the other end side (excluding the protrusion for preventing interference). can do.

[Wave generator]
The wave generator 130 is arranged inside the external gear 120 that meshes from the inside of the internal gear 110, bends the external gear 120, meshes the external tooth 121 with the internal tooth 111, and meshes with the internal tooth 111. It is a member that moves a position (meshing position 101: see FIG. 3) in the circumferential direction. In the case of this embodiment, the wave generator 130 includes a flexible bearing 131 and an elliptical cam 136.

The flexible bearing 131 has flexibility. The flexible bearing 131 includes an inner ring 132 fixedly arranged on the outer peripheral surface of the elliptical cam 136, an outer ring 133 arranged radially inside the external gear 120, a plurality of balls 134, and a cage 135. It has. Of the inner ring 132 and the outer ring 133, at least the outer ring 133 has flexibility.

A convex curved surface portion 139 formed in a convex curved surface shape is provided on the outer peripheral surface of the outer ring 133. The convex curved surface portion 139 is a convex strip portion continuous over the entire circumference of the outer ring 133. The convex curved surface portion 139 is a smooth convex curved surface as a whole. The convex curved surface portion 139 is provided over the entire width of the outer peripheral surface of the outer ring 133. The convex curved surface portion 139 is formed in a wider range than the concave curved surface portion 128 of the external gear 120, and the concave curved surface portion 128 is housed in the convex curved surface portion 139 in the X-axis direction. The radius of curvature of the convex curved surface portion 139 in FIG. 2 as a whole is constant. The radius of curvature of the convex curved surface portion 139 is larger than the radius of curvature of the concave curved surface portion 128. Therefore, the convex curved surface portion 139 is in contact with the concave curved surface portion 128 at two positions at a predetermined interval in the axial direction (Z-axis direction).

An inner ring side raceway groove 1321 that fits into the ball 134 is formed on the outer peripheral surface of the inner ring 132. An outer ring side raceway groove 1331 is formed on the inner peripheral surface of the outer ring 133.

The ball 134 is interposed between the inner ring side raceway groove 1321 and the outer ring side raceway groove 1331. The balls 134 are sandwiched between the inner ring 132 and the outer ring 133 so as to be able to rotate and revolve while being separated from each other by the cage 135.

In the case of the present embodiment, the flexible bearing 131 has a perfect circular shape when it is not fitted to the elliptical cam 136.

The elliptical cam 136 is an elliptical rigid body arranged radially inside the flexible bearing 131. The elliptical cam 136 has an elliptical outer shape with the Y-axis direction as the long axis and the X-axis direction as the short axis. Specifically, the elliptical cam 136 is formed in an elliptical ring shape, and is fixed to the opening 137 by press-fitting or screwing an input shaft body (not shown). The opening 137 of the elliptical cam 136 is a two-stage opening, and the negative side in the Z-axis direction is a circular small-diameter portion, and the positive side in the Z-axis direction is a circular large-diameter portion having a larger diameter than the small-diameter portion. ing.

[Operation of strain wave gearing]
Next, the operation of the wave gearing device 100 will be described. The inner ring 132 of the flexible bearing 131 is elliptically bent by the elliptical cam 136, and the outer ring 133 is elliptically bent by the inner ring 132 via the ball 134. As a result, the wave generator 130 bends the body portion 124 of the external gear 120 into a substantially elliptical shape, and at the same time, the external teeth 121 of the external gear 120 are bent at two meshing positions 101 corresponding to the elliptical major axis portion. It meshes with the internal teeth 111 of the internal gear 110 (see FIG. 3). At this time, at the portion corresponding to the elliptical minor diameter portion, the external teeth 121 of the external gear 120 and the internal teeth 111 of the internal gear 110 are separated from each other and are not subjected to a radial load.

In the above state, when the input shaft body rotates at a relatively high speed, it is bent into an elliptical shape by the wave generator 130 and meshes with the internal teeth 111 of the internal gear 110 at two points in the circumferential direction. The meshing position 101 of the outer teeth 121 of the tooth gear 120 moves in the circumferential direction. Since the numbers of the external teeth 121 and the internal teeth 111 are different, relative rotation corresponding to the difference in the number of teeth occurs between the external gear 120 and the internal gear 110. This rotation is significantly reduced compared to the input rotation speed. The deceleration rotation is output from the output shaft body.

Here, the deformation of the external gear 120 during the operation of the strain wave gearing 100 will be described. FIG. 4 is an enlarged cross-sectional view showing a part of the body portion 124 of the external tooth gear 120 according to the embodiment. In FIG. 4, the body portion 124 when there is no load is shown by a solid line, and the body portion 124 when deformed is shown by a two-dot chain line.

When there is no load, the external gear 120 is not deformed, and the convex curved surface portion 139 of the outer ring 133 of the flexible bearing 131 is in the axial direction (Z-axis direction) with respect to the concave curved surface portion 128 of the external gear 120. ) Are in contact with each other at two locations with a predetermined interval. Thereby, the axial position of the flexible bearing 131 is determined.

On the other hand, when the strain wave gearing device 100 is in operation, the flexible bearing 131 is elastically deformed to rotate the external gear 120. At this time, the external gear 120 is also elastically deformed, and a part of the body portion 124 is inclined with respect to the axial direction (see the two-dot chain line portion in FIG. 4). In this way, even if the body portion 124 is tilted, the concave curved surface portion 128 of the body portion 124 is determined in the axial direction with respect to the convex curved surface portion 139 while sliding on the convex curved surface portion 139 of the outer ring 133. The state of contact is maintained at two places with an interval of. In this way, since the contact points between the flexible bearing 131 and the external gear 120 are maintained at two places, the load on the flexible bearing 131 can be dispersed.

Here, the inclination of the body portion 124 ^{can be estimated by Tan -1} (σ / L). L is the length from the other end of the external gear 120 to the center position of the flexible bearing 131 in the Z-axis direction (see FIG. 1). Further, σ is the amount of deformation of the external tooth gear 120 with respect to the body portion 124 when no load is applied in the X-axis direction of the body portion 124 (see FIG. 4). The radius of curvature of the concave curved surface portion 128 may be obtained so as to follow this inclination.

[Effects, etc.]
As described above, according to the present embodiment, in the external gear 120 that elastically deforms during the rotational operation, the concave curved surface portion 128 has a predetermined distance in the axial direction with respect to the convex curved surface portion 139 of the flexible bearing 131. There are two places where they are in contact with each other. Therefore, even when the external gear 120 is not loaded or deformed, the concave curved surface portion 128 of the external gear 120 and the convex curved surface portion 139 of the flexible bearing 131 continue to be in contact with each other at two points. The load can be distributed. Therefore, wear caused by deformation of the external gear 120 can be suppressed.

Further, since the concave curved surface portion 128 of the external gear 120 and the convex curved surface portion 139 of the flexible bearing 131 are provided with two contact points in the axial direction, the flexible bearing 131 can be moved in the axial direction. It can be suppressed. Therefore, the flexible bearing 131 can be prevented from falling off.

[others]
The present invention is not limited to the above embodiment. For example, another embodiment realized by arbitrarily combining the components described in the present specification and excluding some of the components may be the embodiment of the present invention. The present invention also includes modifications obtained by making various modifications that can be conceived by those skilled in the art within the scope of the gist of the present invention, that is, the meaning indicated by the wording described in the claims, with respect to the above-described embodiment. Is done. In the following description, the same parts as those in the above embodiment may be designated by the same reference numerals and the description thereof may be omitted.

For example, in the above embodiment, the cup type wave gear device has been illustrated and described, but the feature portion of the present invention can also be applied to a so-called top hat type gear device.

Further, in the external gear 120, the connection portion between the rim portion 125 and the flange portion 122 may be R-chamfered or C-chamfered, or may not be chamfered.

Further, in the above embodiment, the case where the radius of curvature of each of the concave curved surface portion 128 and the convex curved surface portion 139 is constant has been illustrated. However, the radii of curvature of the concave curved surface portion 128 and the convex curved surface portion 139 may be partially different.

FIG. 5 is a cross-sectional view showing a concave curved surface portion 128a and a convex curved surface portion 139a according to the first modification. In the concave curved surface portion 128a shown in FIG. 5, the radius of curvature R21 of the end portion on the other end side on the flange portion 122 side is larger than the radius of curvature R22 of the end portion on the one end portion side. Further, in the convex curved surface portion 139a, the radius of curvature R31 of the end portion on the other end side on the flange portion 122 side is larger than the radius of curvature R32 of the end portion on the one end portion side.

When the body portion 124 of the external tooth gear 120 is deformed and tilted, a large load acts on the flange portion 122 side. In order to alleviate this surface pressure, in the concave curved surface portion 128a, the radius of curvature R21 of the end portion on the other end side is made larger than the radius of curvature R22 of the end portion on the one end portion side, and in the convex curved surface portion 139a, the radius of curvature R22 is increased. The radius of curvature R31 at the end on the other end side is made larger than the radius of curvature R32 at the end on the one end side. As a result, the contact area can be increased and the surface pressure can be relaxed at the contact portion on the flange portion 122 side. If at least one of the concave curved surface portion 128a and the convex curved surface portion 139a is satisfied, a constant surface pressure relaxation effect can be obtained.

Further, in the above embodiment, the case where the concave curved surface portion 128 is formed on the inner peripheral surface of the external gear 120 and the convex curved surface portion 139 is formed on the outer peripheral surface of the flexible bearing 131 is illustrated. However, the concave curved surface portion may be formed on the outer peripheral surface of the flexible bearing 131, and the convex curved surface portion may be formed on the inner peripheral surface of the external gear 120.

FIG. 6 is an enlarged cross-sectional view showing a part of the strain wave gearing device 100b according to the second modification. Specifically, FIG. 6 is a diagram corresponding to FIG. 2. As shown in FIG. 6, in the strain wave gearing device 100b according to the second modification, the convex curved surface portion 128b is formed on the inner peripheral surface of the body portion 124b of the external tooth gear 120b. Further, a concave curved surface portion 139b is formed on the outer peripheral surface of the outer ring 133b of the flexible bearing 131b. The radius of curvature of the convex curved surface portion 128b is larger than the radius of curvature of the concave curved surface portion 139b. Therefore, the convex curved surface portion 128b is in contact with the concave curved surface portion 139b at two locations at a predetermined interval in the axial direction (Z-axis direction).

From a manufacturing point of view, as in the above embodiment, the concave curved surface portion 128 is formed on the inner peripheral surface of the external gear 120, and the convex curved surface portion 139 is formed on the outer peripheral surface of the flexible bearing 131. It is preferably formed.

Further, the convex curved surface portion and the concave curved surface portion do not have to be curved as a whole. Specifically, the portion corresponding to the two contact portions may be curved, and the region between them may be planar.

The present invention can be used as a speed reducer or a speed increaser.

100, 100b ... Wave gear device, 101 ... Mating position, 110 ... Internal gear, 111 ... Internal tooth, 112 ... Through hole, 120, 120b ... External gear, 121 ... External tooth, 122 ... Flange, 123 ... Bolt Parts, 124, 124b ... Body, 125 ... Rim, 126 ... Through holes, 128, 128a, 139b ... Concave curved surface, 128b, 139, 139a ... Convex curved surface, 130 ... Wave generator, 131, 131b ... Possible Flexible bearing, 132 ... inner ring, 133 ... outer ring, 134 ... ball, 135 ... cage, 136 ... elliptical cam, 137 ... opening, 200 ... bolt, 1321 ... inner ring side raceway groove, 1331 ... outer ring side raceway groove

Claims (4)

Cylindrical internal gear with multiple internal teeth on the inner peripheral surface,
Cylindrical flexible external gear with multiple external teeth on the outer peripheral surface,
Wave generation that is arranged inside the external gear and bends the external gear in an elliptical shape to mesh the external teeth of the long diameter portion with the internal teeth of the internal gear to move the meshing position in the circumferential direction. Equipped with a vessel
The wave generator
With an elliptical cam
A flexible bearing arranged on the outer peripheral surface of the elliptical cam is provided.
One of the inner peripheral surface of the external gear and the outer peripheral surface of the flexible bearing has a concave curved surface portion formed in a concave curved surface shape.
The other of the inner peripheral surface of the external gear and the outer peripheral surface of the flexible bearing has a convex curved surface portion formed in a convex curved surface shape.
The convex curved surface portion and the concave curved surface portion are in contact with each other at two points at predetermined intervals in the axial direction.
Strain wave gearing. The external tooth gear has the plurality of external teeth at one end and a flange at the other end.
In the concave curved surface portion, the radius of curvature on the other end side is larger than the radius of curvature on the one end side.
The strain wave gearing according to claim 1. The external tooth gear has the plurality of external teeth at one end and a flange at the other end.
In the convex curved surface portion, the radius of curvature on the other end side is larger than the radius of curvature on the one end side.
The strain wave gearing according to claim 1 or 2. The concave curved surface portion is formed on the outer peripheral surface of the flexible bearing.
The convex curved surface portion is formed on the inner peripheral surface of the external gear.
The strain wave gearing according to any one of claims 1 to 3.

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