TW202338231A - Wave motion gear device capable of improving the overall rigidity of the wave motion gear device and improving the power transmission efficiency - Google Patents

Abstract

The present invention provides a wave motion gear device, which improves the overall rigidity of the wave motion gear device and improves the power transmission efficiency. The wave motion gear device includes: an internal meshing gear 2; an external meshing gear 3, which is flexible; and a wave generator 4, which forms a meshing portion P with the internal meshing gear 2 on the external meshing gear 3 and enables the meshing portion P to move in the circumferential direction of the internal meshing gear 2. The wave generator 4 is configured such that the meshing portions P are formed at three or more places in the circumferential direction of the external meshing gear 3. The value (DpF/ZF) obtained from dividing the meshing pitch circle diameter DpF of the external meshing gear 3 by the number of teeth ZF is greater than the value (DpR/ZR) obtained from dividing the meshing pitch circle diameter DpR of the internal meshing gear 2 by the number of teeth ZR.

Description

Wave gear device

The present invention relates to a wave gear device.

Conventionally, as a method of improving the power transmission efficiency of the wave gear device, for example, focusing on the meshing of the internal gear and the external gear, setting the tooth profile of the internal gear and the tooth profile of the external gear (for example, refer to Patent Document 1 and Patent Document 2).

Furthermore, the conventional wave gear device includes a wave generator having a three-lobe shape in which the meshing portions of the internal gear and the external gear are formed in three places (see, for example, Patent Document 3). When the wave gear device has three or more meshing parts, it is effective in improving the rigidity against torsion. [Prior art documents] [Patent Document]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2017-166649 [Patent Document 2] Japanese Patent Application Publication No. 2018-159458 [Patent Document 3] Japanese Patent Relisting No. 2018/025296

[Problem to be solved by the invention]

However, when the number of meshing portions is three or more, large deformations occur in the flexible external meshing gear and the elastic bearing constituting a part of the wave generator. Therefore, there is still room for improvement in improving power transmission efficiency in a wave gear device having three or more meshing parts.

The object of the present invention is to provide a wave gear device that improves the overall rigidity of the wave gear device and improves the power transmission efficiency. [Means to solve the problem]

The wave gear device of the present invention includes: an internal gear; an external gear that is flexible and arranged on the inner circumference side of the internal gear; and a wave generator that is assembled on the inner circumference of the external gear. As a result, the external meshing gear is deflected into a non-circular shape, a meshing portion with the internal meshing gear is formed on the external meshing gear, and the meshing portion is moved in the circumferential direction of the internal meshing gear, and the wave occurs. The device is configured such that the meshing portions are formed at three or more places in the circumferential direction of the external meshing gear. In a state before assembling the external meshing gear to the wave generator, the meshing portion of the external meshing gear is The value obtained by dividing the pitch diameter Dp _F by the number of teeth Z _F of the external gear (Dp _F /Z _F ) is greater than the value obtained by dividing the meshing pitch diameter Dp _R of the internal gear by the number Z _R of the teeth of the internal gear. Value (Dp _R /Z _R ). According to the wave gear device of the present invention, the overall rigidity of the wave gear device can be improved and the amount of deformation required during meshing can be reduced, thereby improving the power transmission efficiency.

In the wave gear device of the present invention, the addendum circle diameter Da _R , the root circle diameter Dd _R and the number of teeth Z _R of the internal gear, the addendum circle diameter Da _F and the teeth of the external gear are preferably The root circle diameter Dd _F and the number of teeth Z _F , and the lifting amount D of the meshing pitch circle of the external gear generated by assembling the external gear to the wave generator satisfy 1<{Z _R ·(Da _R + Dd _R + Da _F + Dd _F -4D)}/{Z _F · (Da _R + Dd _R + Da _F + Dd _F +4D)}≦1.11. In this case, three or more meshing parts can be reliably ensured, and the power transmission efficiency can be improved.

In the wave gear device of the present invention, a material containing a resin material can be used for at least one of the internal gear and the external gear. In this case, the weight of the wave gear device can be reduced, and the cost of the wave gear device can be reduced.

In the wave gear device of the present invention, it is preferable that the teeth of at least one of the internal gear and the external gear are subjected to a friction reduction process. In this case, the power transmission efficiency can be further improved. [Effects of the invention]

According to the present invention, it is possible to provide a wave gear device in which the overall rigidity of the wave gear device is improved and the power transmission efficiency is improved.

Hereinafter, a wave gear device as an embodiment of the present invention will be described with reference to the drawings.

In FIG. 1 , reference numeral 1 denotes a wave gear device as an embodiment of the present invention. The wave gear device 1 includes a ring gear 2 , a flexible external gear 3 arranged on the inner peripheral side of the ring gear 2 , and a wave generator 4 . The wave generator 4 is assembled to the inner periphery of the external gear 3 so that the external gear 3 is deflected into a non-circular shape, a meshing portion P with the internal gear 2 is formed in the external gear 3, and the meshing portion P moves in the circumferential direction of the ring gear 2 .

The wave generator 4 is configured such that meshing portions P are formed at three or more places in the circumferential direction of the external meshing gear 3 . Referring to FIG. 1 , in this embodiment, the external gear 3 has three meshing portions P. In this embodiment, the internal gear 2 and the external gear 3 are coaxially arranged with the axis O as the same axis. That is, in this embodiment, the circumferential direction of the ring gear 2 and the external gear 3 coincides with the direction around the axis O.

In FIG. 2 , the internal gear 2 and the external gear 3 are schematically shown in a state before the external gear 3 is assembled in the wave generator 4 .

Referring to Fig. 2, the ring gear 2 has a plurality of internal teeth 2a and an annular body 2b. The plurality of internal teeth 2a protrude radially inward from the inner circumference of the annular body 2b. In this embodiment, the ring gear 2 is fixed to, for example, a housing of the wave gear device 1 . That is, in this embodiment, the ring gear 2 is a fixed gear. Furthermore, in this embodiment, the ring gear 2 is a rigid gear having high rigidity. The internal gear 2 is made of, for example, iron-based materials such as cast iron, alloy steel, carbon steel, or light metal materials such as magnesium alloy, aluminum alloy, titanium alloy, polyether ether ketone (PEEK), or polyphenylene sulfide. PPS), polyoxymethylene (POM) and other engineering plastics and other resin materials.

Furthermore, referring to Fig. 2, the external gear 3 has a plurality of external teeth 3a and an annular body 3b. The plurality of external teeth 3a protrude radially outward from the outer periphery of the annular body 3b. The external gear 3 is a flexible gear having flexibility. The external gear 3 can be mechanically deformed and restored, for example, by forming the annular body 3b into a thin wall. When the annular body 3 b is formed into a thin wall, metal or resin materials can be used as the material for forming the external gear 3 . Moreover, the external gear 3 can also be deformed and restored by using a flexible material (such as thin-walled materials including alloy steel, carbon steel, light metal, or resin materials such as engineering plastics).

Referring back to FIG. 1 , in this embodiment, the wave generator 4 includes a wave generation core 5 and an elastic bearing 6 .

The wave generating core 5 is connected to a power source such as a motor (not shown). For example, the wave generating core 5 functions like a cam. In this embodiment, the rotation axis of the motor and the axis O are coaxial. Thereby, the wave generating core 5 can rotate around the axis O. The wave generation core 5 has a non-circular shape. In the present embodiment, the wave generation core 5 has a shape having three top portions 5a protruding radially outward, a so-called three lobe shape. In this embodiment, the wave generating core 5 is a member with high rigidity like the ring gear 2 .

The elastic bearing 6 allows relative rotation between the inner circumference of the external gear 3 and the outer circumference of the wave generation core 5 . In this embodiment, the elastic bearing 6 is a ball bearing having an inner ring 6a, an outer ring 6b, and balls 6c. Examples of the ball bearing include deep groove ball bearings. In this embodiment, the inner ring 6a and the outer ring 6b have flexibility. Thereby, the inner ring 6a and the outer ring 6b can respectively deform according to the contour shape of the component to which they are mounted.

The inner ring 6a of the elastic bearing 6 is mounted on the outer periphery of the wave generating core 5. Thereby, the elastic bearing 6 is assembled to the wave generation core 5 so that the shape of the elastic bearing 6 becomes the outline shape of the wave generation core 5 . Furthermore, the outer ring 6 b of the elastic bearing 6 is attached to the inner circumference of the external gear 3 . The external gear 3 is flexible. Thereby, the external gear 3 is assembled to the wave generation core 5 via the elastic bearing 6 so that the shape of the external gear 3 becomes the outline shape of the wave generation core 5 . Therefore, in this embodiment, as shown in FIG. 1 , the external gear 3 is bent into a non-circular three lobe shape according to the outer peripheral shape of the wave generation core 5 . Thereby, meshing portions P with the ring gear 2 are formed on the outer gear 3 at three places in the circumferential direction of the outer gear 3 at intervals of 120 degrees.

In the wave gear device 1 , when the wave generator 4 is rotated, the wave generation core 5 of the wave generator 4 can rotate relatively with respect to the external gear 3 . In the wave gear device 1 , there is a difference in the number of teeth between the number ZF of the external teeth 3 a of the external gear 3 and the number ZR of the internal teeth 2 a of the ring gear 2 . Therefore, when the wave generator 4 is rotated, relative rotation caused by the difference in the number of teeth occurs between the ring gear 2 and the outer gear 3 . In this embodiment, the ring gear 2 is fixed. Accordingly, when the wave generator 4 is rotated, the meshing portion P of the external gear 3 moves in the circumferential direction of the ring gear 2 in the opposite direction to the rotation direction of the wave generator 4 . In this embodiment, every time the wave generating core 5 rotates 120 degrees around the axis O, the meshing portion P moves relative to the ring gear 2 in the opposite direction to the rotation direction of the wave generator 4 . That is, in this embodiment, the input rotation from the wave generator 4 is reversely outputted as the decelerated rotation from the external gear 3 .

In FIG. 3 , a part of the external gear 3 in FIG. 2 is enlarged and shown. In FIG. 3 , the addendum circle, the tooth root circle, and the meshing pitch circle of the external meshing gear 3 are shown in a state where the external meshing gear 3 is annular. Furthermore, in FIG. 3 , symbol Dp _F represents the meshing pitch circle diameter of the external gear 3 .

In FIG. 4 , a part of the ring gear 2 in FIG. 2 is enlarged and shown. FIG. 4 shows the addendum circle, the tooth root circle and the meshing pitch circle of the ring gear 2 . Furthermore, in FIG. 4 , symbol Dp _R represents the meshing pitch circle diameter of the ring gear 2 .

As shown in FIG. 2 , in a state before the external gear 3 is assembled to the wave generator 4 , the meshing pitch circle diameter Dp _F of the external gear 3 is divided by the number of teeth Z _F of the external gear 3 (Dp _F /Z _F ) is greater than the value obtained by dividing the meshing pitch circle diameter Dp _R of the ring gear 2 by the number of teeth Z _R of the ring gear 2 (Dp _R /Z _R ). If expressed numerically, it is as follows.

Dp _F /Z _F ＞Dp _R /Z _R ···（1）

The previous wave gear device did not pay attention to the relationship between the meshing pitch circle diameter Dp _R of the ring gear 2 and the meshing pitch circle diameter Dp _F of the external gear 3 .

In contrast, the wave gear device 1 of this embodiment is a novel wave gear device set based on the relationship between the meshing pitch circle diameter Dp _R of the ring gear 2 and the meshing pitch circle diameter Dp _F of the external gear 3 . According to the wave gear device 1, specifically, the following effects are exerted.

As shown in FIG. 1 , according to the wave gear device 1 of this embodiment, there are three or more meshing portions P (three in this embodiment). Therefore, in this embodiment, compared with the so-called two-lobe shaped wave gear device in which the meshing portion P is two places, the number of meshing parts of the ring gear 2 and the outer mesh gear 3 is increased. That is, according to the wave gear device having a shape of three or more lobes, the meshing portion of the entire wave gear device 1 becomes wider compared to the wave gear device having a shape of two lobes. Furthermore, according to the wave gear device having a shape of three lobes or more, since the meshing portion of the entire wave gear device becomes wider, the machining accuracy of the entire gear is averaged. Therefore, according to the wave gear device having a shape of three or more lobes, the accuracy of angle transmission performed by the wave gear device becomes good. Furthermore, according to the wave gear device having a shape of three or more lobes, the number of meshing portions P is three or more (three places in this embodiment), thereby reducing the torsion generated in the entire wave gear device. That is, according to the wave gear device having a shape with three or more lobes, the rigidity against torsion generated in the entire wave gear device can be improved.

Therefore, according to the wave gear device 1 having a shape of three or more lobes, angle transmission accuracy and impact resistance can be improved compared to a wave gear device having two meshing portions P. Specifically, by having the meshing portions P at three or more places, compared with a wave gear device having two meshing portions P, the rigidity against possible torsion of the external meshing gear 2 can be improved, and the structure of the wave generator can be improved. The elastic bearing 4 in part 6 may produce torsional rigidity. Thereby, according to the wave gear device 1, compared with a wave gear device having two meshing portions P, the angle transmission accuracy and impact resistance can be improved.

On the other hand, referring to FIG. 1 , in the case of a wave gear device having a shape of three lobes or more, the deformation of the elastic bearing 6 in the meshing portion P becomes deformation with a small radius of curvature, that is, a large bending deformation. . In this case, a large bending stress is generated in the elastic bearing 6, so there is room for improvement in the durability of the elastic bearing 6 and even the durability of the wave gear device. Moreover, such large bending deformation occurs in the elastic bearing 6, causing the track of the ball 6c to change significantly. Therefore, in the wave gear device having a shape of three or more lobes, the resistance caused by the movement of the ball 6c increases. That is, for a wave gear device having a shape of three lobes or more, there is still room for improvement in the power transmission efficiency of the wave gear device.

On the other hand, according to the wave gear device 1 of this embodiment, the deformation of the elastic bearing 6 can be reduced by setting the ring gear 2 and the external gear 3 so as to satisfy the above-mentioned equation (1). Thereby, according to the wave gear device 1 of this embodiment, the power transmission efficiency can be improved compared to a wave gear device having a shape of three or more lobes that is not set to satisfy the above equation (1). Specifically, by setting the internal meshing gear 2 and the external meshing gear 3 so as to satisfy the above equation (1), compared with the wave gear device in which the meshing portion P is at two places, it is possible to suppress the possible occurrence of the external meshing gear 3 deformation amount, and suppress the possible deformation amount of the elastic bearing 6. Thereby, according to the wave gear device 1 , the power transmission efficiency can be improved compared to a wave gear device having a shape of three or more lobes that is not set to satisfy the above-described equation (1).

Therefore, according to the wave gear device 1 of this embodiment, the rigidity of the entire wave gear device can be improved and the power transmission efficiency can be improved.

In this embodiment, preferred are the addendum circle diameter Da _R , the dedendum circle diameter Dd R and the number of teeth Z _R of the internal gear 2 , the addendum circle diameter Da _F , the dedendum circle diameter Dd _{F and} the external gear 3 . The number of teeth Z _F and the lifting amount D (refer to FIG. 1 ) of the meshing pitch circle of the external gear 3 produced by assembling the external gear 3 to the wave generator 4 satisfy the following relationship. For example, referring to FIGS. 1 and 2 , the lift amount D is the tip circle radius of the external teeth 3 a of the long axis portion of the external gear 3 when the wave generator 4 is inserted into the inner circumference of the external gear 3 (Fig. The long radius R3a of 1) is the same as the addendum circle radius of the external teeth 3a of the external gear 3 in a perfect circular state before the wave generator 4 is inserted into the inner circumference of the external gear 3 (the addendum circle radius in Figure 2 r3) difference.

1＜{Z _R ·（Da _R ＋Dd _R ＋Da _F ＋Dd _F －4D）}/{Z _F ·（Da _R ＋Dd _R ＋Da _F ＋Dd _F ＋4D)}≦1.11···(2)

When the relationship of equation (2) is satisfied, three or more meshing parts can be reliably secured and the power transmission efficiency can be improved.

Generally speaking, the meshing pitch circle diameter Dp _R of the internal meshing gear 2 and the meshing pitch circle diameter Dp _F of the external meshing gear 3 are represented by equations (3a) to (6b).

This is a basic calculation formula for calculating the meshing pitch circle diameter Dp _R of the internal gear 2 and the meshing pitch diameter Dp _F of the external gear 3 . External gear: Dp _F = (Da _R + Dd _R + Da _F + Dd _F )/4-D···(3a) Internal gear: Dp _R = (Da _R +Dd _R +Da _F +Dd _F )/4+D···( 3b)

This is another calculation formula for calculating the meshing pitch circle diameter Dp _R of the internal meshing gear 2 and the meshing pitch circle diameter Dp _F of the external meshing gear 3 . External gear: Dp _F ＝Da _F -2·f _ha ·m＝（Da _R ＋Da _F )/2－D···(4a) Internal gear: Dp _R ＝Da _R ＋2·f _ha ·m＝（ Da _R + Da _F )/2 + D···（4b）

This is another calculation formula for calculating the meshing pitch circle diameter Dp _R of the internal meshing gear 2 and the meshing pitch circle diameter Dp _F of the external meshing gear 3 . External gear: Dp _F ＝Dd _F ＋2·f _hd ·m＝（Dd _R ＋Dd _F )/2－D···（5a） Internal gear: Dp _R ＝Dd _R －2·f _hd ·m＝（ Dd _R + Dd _F )/2 + D···（5b）

Furthermore, the meshing pitch circle circumference of the ring gear 2 and the meshing pitch circle circumference of the external meshing gear 3 are expressed as follows.

The meshing pitch circle circumference of the external meshing gear 3: π·Dp _F ···(6a) The meshing pitch circle circumference of the internal meshing gear 2: π·Dp _R ···(6b) Furthermore, equations (6a) and (6a) In 6b), π is pi.

Furthermore, the distance between the internal teeth 2a of the ring gear 2 and the distance between the external teeth 3a of the external gear 3 are expressed as follows.

The distance between the teeth 3a of the external gear 3: π·Dp _F /Z _F =π·(m ₃ +2·X _F ·m ₃ /Z _F )···(7a) The distance between the teeth 2a of the internal gear 2: π·Dp _R /Z _R =π·(m ₂ -2·X _R ·m ₂ /Z _R )···(7b)

In Formula (7a) and Formula (7b), π is pi. Therefore, π in equation (7a) is the same as that in equation (7b). Moreover, in formula (7a), m ₃ is the module of the external gear 3. Moreover, in formula (7b), m ₂ is the module of the ring gear 2. Since the internal gear 2 and the external gear 3 are in mesh, the module m ₂ and the module m ₃ are the same as the pi (m ₂ =m ₃ ). In addition, X _F is the displacement coefficient of the tooth 3a of the external gear 3. Furthermore, X _R is the transfer coefficient of the teeth 2 a of the ring gear 2 .

That is, under the condition that equation (1) is established, as shown by equations (7a) and (7b), in the wave gear device of the present invention, the distance between the external teeth 3a of the external gear 3 is smaller than that of the internal gear 2 The internal teeth 2a are further spaced apart. That is, when the external gear 3 is incorporated into the wave gear device 1 as an element of the wave gear device 1 , the meshing position of the external teeth 3 a of the external gear 3 is further toward the tip direction (closer to the center of the internal gear 2 direction) offset position, meshing with the internal gear 2. Therefore, the lifting amount D of the meshing pitch circle may be a small value. That is, according to the present invention, the lifting amount D of the meshing pitch circle can be set to a small value, thereby reducing the amount of deformation required during meshing. As a result, the power transmission efficiency of the wave gear device 1 is improved.

Furthermore, as an example of making equation (1) hold, in the case of m ₂ =m ₃ , as long as a general displacement coefficient satisfying X _F /Z _F + X _R /Z _R > 0 is applied to the ring gear 2 and External gear 3 is sufficient.

Furthermore, the upper limit value of the parameter X=(Dp _F /Z _F )/(Dp _R /Z _R ) is preferably X=1.11.

When the above-mentioned formula (1) is divided by (Dp _R /Z _R ), the parameter X is as follows. X>1···(8)

Next, referring to FIG. 1 , the circumferential direction between the meshing portion P of the external gear 3 and the tooth addendum of the internal teeth 2a of the ring gear 2 and the tooth addendum of the external teeth 3a of the external gear 3 are defined. The maximum distance in the radial clearance (hereinafter also referred to as the "maximum tooth tip distance") is set to C, and calculation is performed when the meshing pitch circle diameter Dp _R of the internal gear 2 and the meshing pitch diameter Dp _F of the external gear 3 are changed. , the relationship between the maximum tooth tip distance C and the parameter X. In FIG. 5 , the calculation results are shown in a graph as a relationship between the maximum tooth tip distance C and the parameter X.

Furthermore, in the above calculation, regarding the module m of the gears, the module m ₂ of the internal gear 2 and the module m ₃ of the external gear 3 are equal, which is m=0.3. The number Z _F of the external teeth 3 a of the external gear 3 is Z _F =48. The number Z _R of the internal teeth 2 a of the ring gear 2 is Z _R =51. Regarding the addendum height coefficient f _ha of the gear, the addendum height coefficient f _ha2 of the internal teeth 2 a of the ring gear 2 is equal to the addendum height coefficient f _ha3 of the external teeth 3 a of the external gear 3 , which is f _ha =1. Regarding the tooth root height coefficient f _hd of the gear, the tooth root height coefficient f _hd2 of the internal teeth 2 a of the ring gear 2 is equal to the tooth root height coefficient f _hd3 of the external teeth 3 a of the external gear 3 , which is f _hd =1.25.

Referring to the graph of FIG. 5 , when the vertical axis is 0 (zero), the maximum tooth tip interval C becomes C = 0 (zero). Therefore, in the portion where the gap should originally occur, the tooth tip of the internal tooth 2a of the ring gear 2 It comes into contact with the tooth tips of the external teeth 3a of the external gear 3. Referring to FIG. 1 , if the parameter (short radius R3b in Figure 1) becomes larger, causing the maximum radial gap C to decrease. That is, when the vertical axis is 0 (zero), the tooth tops of the internal teeth 2 a of the ring gear 2 and the tooth tops of the external teeth 3 a of the external gear 3 interfere with the portion other than the meshing portion P. Therefore, when the maximum radial clearance C is C=0 (zero), the wave gear device 1 does not function. Referring to FIG. 5 , if X=1.11 is exceeded, the vertical axis becomes 0 or less. Therefore, if the above-mentioned expression (2) is satisfied, three or more meshing portions P can be reliably ensured. Thereby, when the relationship of equation (2) is satisfied, three or more meshing parts can be reliably ensured and the power transmission efficiency can be improved.

FIG. 6 is a diagram schematically showing the tooth addendum height fha·m and the tooth root height fhd·m of the gear. As shown in FIG. 6 , in this embodiment, the tooth top height of the gear is represented by fha·m, and the tooth root height is represented by fhd·m.

In this embodiment, it is preferable that at least one of the internal gear 2 and the external gear 3 contains a resin material. In this case, the wave gear device can be lightweight and the cost of the wave gear device can be reduced.

As described above, when the number of meshing portions P is three or more, the rigidity with respect to the torsion of the entire wave gear device is improved, thereby making it less likely to cause torsion of the entire wave gear device. Thereby, when there are three or more meshing portions P, at least one of the ring gear 2 and the outer gear 3 can contain at least a resin material. In this case, by including a resin material in at least one of the ring gear 2 and the external gear 3, the wave gear device 1 can be reduced in weight. Furthermore, in this case, by including a resin material in at least one of the ring gear 2 and the external gear 3, the cost of the wave gear device 1 can be reduced.

Examples of the resin material include engineering plastics such as PEEK, PPS, and POM. Furthermore, "at least one of the internal gear 2 and the external gear 3 contains a resin material" means that a combination of the resin material and a different material is allowed. For example, at least one of the ring gear 2 and the external gear 3 may be formed of a composite material of the resin material and metal. Specifically, for example, the annular body and teeth of the gear may be formed of different materials.

Furthermore, it is preferable that the teeth of at least one of the internal gear 2 and the external gear 3 are subjected to a friction reduction process. In this case, the power transmission efficiency can be further improved.

In this embodiment, by applying low-friction coating to the internal teeth 2a of the ring gear 2, a low-friction layer can be provided on the surface of the internal teeth 2a. The low friction layer may be formed of Diamond Like Carbon (DLC), for example. Furthermore, when friction reduction processing is performed on the teeth of the gear, equations (1) and (2) are based on the dimensions after friction reduction processing.

The above description merely illustrates one embodiment of the present invention, and various changes may be made depending on the scope of the patent application.

1: Wave gear device 2: Internal gear 2a: Internal teeth 2b, 3b: Ring-shaped body 3: External gear 3a: External teeth 4: Wave generator 5: Wave generation core 5a: Top 6: Elastic bearing 6a: Inner ring 6b: Outer ring 6c: Ball C: Maximum tooth tip distance Dp _F , Dp _R : Meshing pitch circle diameter fha m: Tooth tip height fhd m: Tooth root height O: Axis P: Meshing part R3a: Long radius R3b: short radius r3: tip circle radius

FIG. 1 is a diagram schematically showing a wave gear device as an embodiment of the present invention. FIG. 2 is a diagram schematically showing the ring gear and the external gear in a state before the external gear is assembled in the wave generator. FIG. 3 is an enlarged view of a part of the external gear of FIG. 2 . FIG. 4 is an enlarged view of a part of the ring gear in FIG. 2 . FIG. 5 is a graph showing the tooth tip interval C with respect to the parameter X when the meshing pitch circle diameter Dp _R of the internal gear and the meshing pitch diameter Dp _F of the external gear are changed. FIG. 6 is a schematic diagram for explaining the tooth top height and tooth root height of the gear.

1: Wave gear device

2: Internal gear

3: External meshing gear

4: Wave generator

5: Fluctuation generation core

5a: top

6: Elastic bearing

6a:Inner circle

6b: Outer ring

6c: Ball

C: Maximum tooth tip distance

O: axis

P: meshing part

R3a: long radius

R3b: short radius

Claims (4)

A wave gear device includes: an internal gear; an external gear that is flexible and arranged on the inner circumferential side of the internal gear; and a wave generator that is assembled on the inner circumference of the external gear. The external meshing gear is deflected into a non-circular shape, a meshing portion with the internal meshing gear is formed on the external meshing gear, and the meshing portion is moved in the circumferential direction of the internal meshing gear, and the undulation The generator is configured such that the meshing portions are formed at three or more places in the circumferential direction of the external gear. In a state before the external gear is assembled to the wave generator, the external gear has The value obtained by dividing the meshing pitch circle diameter Dp _F by the number of teeth Z _F of the external meshing gear (Dp _F /Z _F ) is greater than the meshing pitch circle diameter Dp _R of the internal meshing gear divided by the number of teeth Z of the internal meshing gear. The value obtained by _R (Dp _R /Z _R ). The wave gear device according to claim 1, wherein the addendum circle diameter Da _R , the root circle diameter Dd R and the number of teeth Z _R of the internal meshing gear, the addendum circle diameter Da _F and the tooth number Z _R of the external meshing gear. The root circle diameter Dd _F and the number of teeth Z _F , and the lifting amount D of the meshing pitch circle of the external gear generated by assembling the external gear to the wave generator satisfy 1<{Z _R ·( Da _R ＋Dd _R ＋Da _F ＋Dd _F －4D）}/{Z _F ·（Da _R ＋Dd _R ＋Da _F ＋Dd _F ＋4D）}≦1.11. The wave gear device according to claim 1 or claim 2, wherein at least one of the internal gear and the external gear contains a resin material. The wave gear device according to any one of claims 1 to 3, wherein a friction reducing process is performed on the teeth of at least one of the internal gear and the external gear.