Patent Application
20190085965
The present invention relates to a transmission and an actuator.
JP-A 2005-308131 describes a cup-shaped strain wave gearing device including a rigid internal gear, a cup-shaped flexible external gear arranged coaxially inside of the rigid internal gear, and a wave generator having an elliptical contour and fitted inside of the flexible external gear. The wave generator of the cup-shaped strain wave gearing device includes a cam plate having an elliptical contour, a plug to which the cam plate is coaxially fixed, and a wave bearing attached to an outer circumferential surface of the cam plate. A shaft hole, in which an input shaft can be inserted and fixed, is defined in a center of the plug.
When the input shaft is press fitted into the shaft hole of the plug, the shape of an outer circumference of the input shaft can be transferred to the plug to deform an outer circumferential portion of the plug. The flexible external gear is deformed in accordance with the shape of the outer circumferential portion of the plug, and therefore, a deformation of the outer circumferential portion of the plug might lead to a deterioration in accuracy with which the rigid internal gear and the flexible external gear mesh with each other.
A transmission according to a preferred embodiment of the present invention includes a first shaft that is rotatable in a circumferential direction about a central axis extending in one direction; a second shaft that is rotatable in the circumferential direction, and arranged in series with the first shaft in an axial direction in which the central axis extends; an internal gear including an internal tooth portion; a housing that houses the internal gear therein; an annular external gear connected to the second shaft, and including an external tooth portion that partially meshes with the internal tooth portion; a cam that rotates together with the first shaft, and including a connection hole that houses a portion of the first shaft; and a bearing located between an inner circumferential surface of the external gear and an outer circumferential surface of the cam. An outer circumferential surface of the portion of the first shaft which is housed in the connection hole includes a recessed portion recessed in radial directions centered on the central axis. At least a portion of the recessed portion is opposite to the external tooth portion in the radial directions.
An actuator according to a preferred embodiment of the present invention includes the transmission according to a preferred embodiment of the present invention and a rotary electric machine connected to one of the first shaft and the second shaft.
Preferred embodiments of the present invention are able to reduce the likelihood of a deformation of the cam, and reduce the likelihood of a deterioration in accuracy with which the internal gear and the external gear mesh with each other.
The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
The structure of the motor 200 will now be described below with reference to
The rotor 210 includes a cylindrical yoke 211, and a permanent magnet 212 fixed to an outer circumferential surface of the yoke 211. A portion of the first shaft 110 extending in the x direction is housed in the yoke 211, and the yoke 211 is fixed to the first shaft 110. The permanent magnet 212 is arranged on an outer circumference of the yoke 211. The permanent magnet 212 is a ring magnet including south and north poles arranged to alternate with each other in the θ direction, and arranged at regular intervals in the θ direction. Each magnetic pole of the permanent magnet 212 is arranged on a surface facing outward in an r direction, i.e., on a surface facing the stator 220.
The stator 220 includes a core 221 and a plurality of coils 222. The core 221 is made of a soft magnetic material, and includes a plurality of teeth 224. The teeth 224 are arranged at regular intervals in the θ direction. Each tooth 224 is arranged to extend in an r direction toward the central axis 111. The number of coils 222 and the number of teeth 224 are equal to each other.
The number of coils 222, that is, the number of slots, is different from the number of poles of the permanent magnet 212. In the case of a three-phase motor, for example, the number of slots is a multiple of three, and the number of poles is an even number.
The motor 200 further includes a casing 230 and a cover 240. The casing 230 includes a tubular portion 231 and a plate-shaped cover portion 232. The tubular portion 231 has a columnar space defined inside thereof, and one end of the tubular portion 231, i.e., an end portion of the tubular portion 231 in the x direction in the example of
The tubular portion 231 of the casing 230 is arranged to have an inside diameter substantially equal to an outside diameter of the core 221. The core 221 is fixed to an inner circumferential surface of the tubular portion 231 through, for example, an adhesive. The stator 220 is thus fixed to an inner circumferential surface of the casing 230. The cover portion 232 includes a circular hole 233 defined in a center thereof in the r directions. The hole 233 is arranged to have a diameter greater than that of the first shaft 110, and the first shaft 110 is arranged to pass through the hole 233. A bearing 234 in the shape of a circular ring is fitted around the hole 233, and the bearing 234 is arranged to rotatably support the first shaft 110.
The casing 230 is arranged to have an external shape being a combination of a semicircle and a rectangle when viewed in the x direction. In other words, the casing 230 includes a semicircular portion 235 and a flange portion 236, which are semicircular and rectangular, respectively, when viewed in the x direction. A semicircular exterior of the semicircular portion 235 is arranged to be concentric with an inner circumferential surface of the semicircular portion 235. That is, the exterior of the semicircular portion 235 is an arc-shaped surface which is semicircular with the central axis of the first shaft 110 as a center. Meanwhile, the flange portion 236 includes two right-angled corner portions 237 each of which projects in an r direction, and the flange portion 236 is joined to the speed reducer 300 through bolts at the corner portions 237.
The cover 240 is a circular plate having a diameter slightly greater than that of a circular opening of the casing 230. The cover 240 is fixed at the opening of the casing 230 to close the opening. The cover 240 includes a circular hole 241 defined in a center thereof in the r directions. A bearing 242 in the shape of a circular ring is fitted in the hole 241. The bearing 242 is arranged to rotatably support the first shaft 110.
Once electric currents are supplied to the coils 222 of the stator 220, which is the armature, in the motor 200 having the above-described structure, action of electromagnetic induction causes the first shaft 110 to rotate in the θ direction.
The structure of the speed reducer 300 will now be described below with reference to
The first shaft 110 is arranged to extend in the x direction from the cover 240, and the wave generator 310 is connected to one end of the first shaft 110. The wave generator 310 includes a cam 304 and a flexible bearing 305.
The cam 304 is fixed to one end portion of the first shaft 110.
The cam 304 includes a connection hole 344 defined in a center thereof in the r directions. The one end portion of the first shaft 110 is housed in the connection hole 344, and the one end portion of the first shaft 110 is fixed in the connection hole 344 (see
The cover portion 332 includes surfaces on both sides in the x direction, and the second shaft 120 is arranged to extend in the x direction from a center in the r directions of one of the surfaces of the cover portion 332 on an opposite side to the surface thereof on which the cylindrical portion 331 is arranged. The external gear 303 is arranged to be coaxial with the first shaft 110, and the second shaft 120 and the first shaft 110 are arranged coaxially in series (see
Reference will now be made to
The cam 304 is a metal block made of, for example, carbon steel, and is arranged to have a high rigidity. Thus, the flexible bearing 305, which is attached to the cam 304, is fitted to an outer circumferential surface of the decreased diameter portion 343 of the cam 304, and is deformed into an elliptical shape. In addition, since an inner circumferential surface of the external gear 303 is in contact with the flexible bearing 305, the cylindrical portion 331 of the external gear 303 is deformed into an elliptical shape matching an exterior of the flexible bearing 305.
Similarly to the casing 230 of the motor 200, the housing 301 is arranged to have a shape being a combination of a semicircle and a rectangle when viewed in the x direction (see
In addition, referring to
Reference will now be made to
The number of teeth of the internal tooth portion 321 of the internal gear 302 is different from the number of teeth of the external tooth portion 333 of the external gear 303. For example, when n denotes a positive integer, the number of teeth of the internal tooth portion 321 is arranged to be greater than the number of teeth of the external tooth portion 333 by 2n. Once the first shaft 110 starts rotating, the cam 304 starts rotating together with the first shaft 110. The rotation of the cam 304 causes the external gear 303 to be elastically deformed such that the major axis of the elliptical shape rotates. Accordingly, meshing positions between the external tooth portion 333 and the internal tooth portion 321 move in the θ direction. That is, the wave generator 310 causes the external gear 303 to be deformed in accordance with the rotation of the first shaft 110 such that meshing positions between the internal gear 302 and the external gear 303 shift in the θ direction. Every time the first shaft 110 completes a single rotation, the external gear 303 rotates in the θ direction by an amount corresponding to a difference between the number of teeth of the internal tooth portion 321 and the number of teeth of the external tooth portion 333. As a result, the rotation of the first shaft 110 is transferred to the second shaft 120 while the speed of the rotation is reduced.
A bearing 306 is attached to the housing 301, and the bearing 306 is arranged to support the second shaft 120 such that the second shaft 120 is capable of rotating about the central axis 111. In addition, a washer 307 and a disk-shaped plate member 308 are attached to the second shaft 120 such that the bearing 306, the washer 307, and the plate member 308 are arranged in the x direction.
An example of the recessed portion 112 is illustrated in
The recessed portion 112 is arranged opposite to the external tooth portion 333 of the external gear 303 in the r directions. More specifically, in the preferred embodiment illustrated in
The diameter of the connection hole 344 before a portion of the first shaft 110 is housed therein is slightly smaller than the diameter of the first shaft 110. The first shaft 110 is press fitted into the connection hole 344 having such a dimension, and the first shaft 110 and the cam 304 are thus connected to each other. When the first shaft 110 is press fitted into the connection hole 344, the shape of an outer circumference of the first shaft 110 can be transferred to the cam 304 to slightly deform the shape of an outer circumference of the cam 304. However, in the range over which the recessed portion 112 extends in the x direction, the cam 304 and the first shaft 110 are not in contact with each other, and the shape of the outer circumference of the first shaft 110 is not transferred to the cam 304. Therefore, in the range over which the recessed portion 112 extends in the x direction, the likelihood of a deformation of the shape of the outer circumference of the cam 304 is reduced.
The flexible bearing 305 is arranged between the recessed portion 112 and the external tooth portion 333. That is, the flexible bearing 305 is arranged opposite to each of the recessed portion 112 and the external tooth portion 333 in the r directions. Therefore, the flexible bearing 305 is arranged at a portion of the outer circumference of the cam 304 where the likelihood of a deformation of the shape of the outer circumference of the cam 304 is reduced, and the external tooth portion 333 is deformed into an elliptical shape matching the shape of the outer circumference of the cam 304 through the flexible bearing 305. Accordingly, an influence of the shape of the outer circumference of the first shaft 110 on the shape of the external tooth portion 333 is reduced to prevent a deterioration in accuracy with which the internal gear 302 and the external gear 303 mesh with each other.
The depth of the recessed portion 112, that is, the dimension of the recessed portion 112 measured in the r directions, is equal to or smaller than a half of a radius of the portion of the first shaft 110 which is housed in the connection hole 344. This contributes to ensuring a sufficient mechanical strength of the first shaft 110 while avoiding an excessive reduction in the dimension, measured in the r directions, of a portion of the first shaft 110 in which the recessed portion 112 is defined.
Speed reducers according to example modifications of the present preferred embodiment will now be described below.
This contributes to preventing a deformation of an outer circumference of the cam 304 caused by the first shaft 110 from affecting the shape of the entire external tooth portion 333. This in turn contributes to more effectively preventing a deterioration in meshing between an internal gear 302 and the external gear 303.
Thus, the first shaft 110 and the cam 304 are not in contact with each other over the range of the recessed portion 112, extending up to an end of the cam 304 on the side on which the large diameter portion 342 lies, and this contributes to more effectively preventing a deformation of the shape of an outer circumference of the cam 304.
This contributes to more effectively preventing a deformation of the shape of an outer circumference of the cam 304. In addition, connection of the first shaft 110 to the cam 304 is made easier because the total area of contact between the cam 304 and the first shaft 110 in the connection hole 344 is reduced.
In the actuator 100 according to the above-described preferred embodiment of the present invention, the first shaft 110 is connected to the motor 200, which is an example of a rotary electric machine. Note, however, that actuators according to other preferred embodiments of the present invention may have another structure. In another preferred embodiment of the present invention, an electric generator, which is another example of a rotary electric machine, may be connected to a first shaft 110. In yet another preferred embodiment of the present invention, a second shaft 120 may be connected to a rotary electric machine, such as, for example, a motor, an electric generator, or a motor generator.
Features of the above-described preferred embodiments and the modifications thereof may be combined appropriately as long as no conflict arises.
While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-102610 | May 2018 | JP | national |
This application claims the benefit of priority to U.S. patent application Ser. No. 62/559,026 filed on Sep. 15, 2017 and Japanese Patent Application No. 2018-102610 filed on May 29, 2018. The entire contents of these applications are hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62559026 | Sep 2017 | US |
