Hollow wave gear device

Abstract

The present invention provides a hollow wave gear device (1), in which a wave generator plug (5a) of a wave generator (5) is integrally formed on a part of a hollow rotating shaft (6). On the hollow rotating shaft (6), a plug reinforcement portion (5d) having a thickness thicker than the wave generator plug (5a) is integrally formed adjacent to the wave generator plug (5a). The wave generator plug (5a) is reinforced by the plug reinforcement portion (5d) having a high rigidity formed adjacent to the wave generator plug (5a). When the hollow rotating shaft (6) is made thinner in order to achieve a light weight and a large diameter of the hollow portion thereof, it is possible to prevent or suppress a reduction in the rigidity of the wave generator plug (5a). As a result, a reduction in ratchet torque can be suppressed.

Description

Technical Field

[0001] The present invention relates to a wave gear device, and more particularly to a hollow wave gear device including a hollow portion extending through a central portion in an axial direction. Background Art

[0002] For example, Patent Document 1 (International Publication No. 2015 / 001582) describes a hollow wave gear device. According to the hollow wave gear device described in Patent Document 1, a flexible top-hat-shaped external gear is coaxially arranged inside a rigid internal gear, a wave generator is coaxially arranged inside the external gear, and a hollow rotating shaft coaxially passes through the center of the wave generator. The wave generator includes: a wave generator plug having an elliptical outer peripheral surface; and a wave generator bearing, which is assembled between the elliptical outer peripheral surface and the inner peripheral surface of the external gear. The wave generator plug is integrally formed with: a hollow rotating shaft serving as an input shaft. That is, an elliptical outer peripheral surface is formed on a part of the circular outer peripheral surface of the hollow rotating shaft, and the shaft portion having the elliptical outer peripheral surface functions as a wave generator plug.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2015 / 001582 Summary of the invention

[0006] In a hollow wave gear device, it is sometimes required to increase the diameter of the hollow portion rather than increase the outer diameter of the device. In addition, it is sometimes required to reduce the thickness of the wave generator plug in order to reduce the weight of the device. If the diameter of the hollow portion integrally formed with the wave generator plug is increased or the hollow rotating shaft or the wave generator plug is reduced in order to meet such a requirement, the torque performance will also be reduced due to the reduction in the rigidity of the wave generator.

[0007] An object of the present invention is to provide a hollow type wave gear device capable of preventing or suppressing a decrease in torque performance when a hollow rotating shaft or a wave generator plug is thinned in order to increase the diameter of a hollow portion or the like.

[0008] In order to solve the above problems, the hollow wave gear device of the present invention has:

[0009] Rigid internal gears;

[0010] an external gear coaxially disposed inside the internal gear and having a flexible cylindrical portion formed with external teeth capable of meshing with the internal teeth of the internal gear;

[0011] a wave generator coaxially disposed inside the cylindrical portion of the external gear, bending and deforming the cylindrical portion into an elliptical shape and meshing with the internal teeth of the internal gear at two locations in the circumferential direction, and once driven to rotate, causing the meshing position between the external teeth and the internal teeth to move in the circumferential direction; and

[0012] A hollow rotating shaft coaxially passes through the wave generator and extends therefrom. The hollow wave gear device is characterized in that:

[0013] The wave generator has:

[0014] A wave generator plug having an elliptical outer peripheral surface;

[0015] a plug reinforcement portion provided to increase the rigidity of the wave generator plug; and a wave generator bearing mounted between the elliptical outer peripheral surface and the inner peripheral surface of the cylindrical portion of the external gear,

[0016] The hollow rotating shaft is integrally formed with a first shaft portion defining the wave generator plug and a second shaft portion defining the plug reinforcement portion.

[0017] In the hollow rotating shaft, the plug reinforcement portion is formed at a position adjacent to the wave generator plug in the direction of the central axis of the hollow rotating shaft,

[0018] The thickness of the plug reinforcement portion in the radial direction is greater than the thickness of the wave generator plug in the radial direction.

[0019] In the hollow type wave gear device of the present invention, a plug reinforcement portion having a thickness thicker than the wave generator plug is formed adjacent to the wave generator plug on the hollow rotating shaft. The wave generator plug is reinforced by the plug reinforcement portion having a high rigidity formed in a dot shape adjacent to the wave generator plug. Even if the hollow rotating shaft is formed to be thinner in order to increase the hollow portion of the hollow rotating shaft, a decrease in the rigidity of the wave generator plug can be prevented or suppressed, thereby suppressing a decrease in torque performance (ratchet torque). In addition, in the hollow rotating shaft, the plug reinforcement portion having a relatively high thickness is only partially formed at a position adjacent to the wave generator plug, so that an increase in weight and an increase in inertia of the hollow rotating shaft can be suppressed to a minimum.

[0020] Here, the inner circumference of the wave generator plug and the plug reinforcement in the hollow rotating shaft is formed as a circular inner circumference with the same diameter at each position in the direction of the central axis. In this case, the outer circumference of the plug reinforcement is formed at each position in the direction of the central axis to have an outer diameter larger than the major diameter of the elliptical shape defining the elliptical outer circumference of the wave generator plug. By forming a thickness protrusion on the outer circumference side of the hollow rotating shaft to form a thick plug reinforcement, the diameter of the hollow portion can be ensured.

[0021] In addition, in the hollow rotating shaft, a thick plug reinforcement portion formed in a dot shape adjacent to the wave generator plug can be used as a counterweight for the wave generator plug. For example, the outer peripheral surface of the plug reinforcement portion is formed into an elliptical outer peripheral surface having a phase difference of 90 degrees with respect to the elliptical outer peripheral surface of the wave generator plug with the central axis as the center.

[0022] Furthermore, in the case of a cup-shaped or top-hat-shaped wave gear device, a dead space can be formed between the inner peripheral surface of the cylindrical portion of the cup-shaped or top-hat-shaped external gear and the outer peripheral surface of the hollow rotating shaft. If a thick plug reinforcement portion is arranged by utilizing this dead space, it is not necessary to change the design of other parts of the wave gear device. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention is applied to a hollow wave gear device, which includes a schematic longitudinal sectional view, a schematic transverse sectional view, and explanatory diagrams showing the outline shape of each part.

[0024] Figure 2 The diagram is a schematic longitudinal sectional view and a schematic transverse sectional view showing an example of a hollow type wave gear device including a plug reinforcement portion.

[0025] Figure 3 It is a schematic longitudinal sectional view showing another example of a hollow type wave gear device including a plug reinforcement portion.

[0026] Figure 4 1 is a schematic longitudinal sectional view and a schematic transverse sectional view showing an example of a cup-type wave gear device including a plug reinforcement portion.

[0027] Explanation of symbols

[0028] 1 Hollow wave gear device 1a Center axis

[0029] 2 Internal gear 2a Internal gear

[0030] 3 External gear 3a External gear

[0031] 3b Cylinder 3c Diaphragm

[0032] 3d boss 4 cross roller bearing

[0033] 4a Inner ring 4b Outer ring

[0034] 5 Wave generator 5a Wave generator plug

[0035] 5b Wave generator bearing 5c ​​Elliptical outer peripheral surface

[0036] 5d Plug reinforcement 6 Hollow rotating shaft

[0037] 6a Shaft end 6d Shaft end

[0038] 6e Circular inner surface 6f Circular outer surface

[0039] 6g Circular outer surface 7 Hollow part of the device

[0040] 21 Hollow wave gear device 21a Center axis

[0041] 25 Wave generator 25a Wave generator plug

[0042] 25b Wave generator bearing 25c Elliptical outer peripheral surface

[0043] 25d Plug reinforcement 26 Hollow rotating shaft

[0044] 26e circular inner circumference 26f circular outer circumference

[0045] 31 Hollow wave gear device 31a Center axis

[0046] 35 Wave generator 35a Wave generator plug

[0047] 35b Wave generator bearing 35c Elliptical outer peripheral surface

[0048] 35d Plug reinforcement portion 35e Circular outer peripheral surface

[0049] 35f Circular inner surface 35g Circular end surface

[0050] 36 Hollow rotating shaft 41 Cup type wave gear device

[0051] 41a Central axis 42 Internal gear

[0052] 42a Internal gear 43 External gear

[0053] 43a External teeth 43b Cylindrical part

[0054] 43c diaphragm 43d boss

[0055] 44 Wave generator 45 Wave generator plug

[0056] 45a: Elliptical outer peripheral surface 45b: Plug cylindrical portion

[0057] 45c Rib 45d Inner cylindrical portion

[0058] 45e Shaft hole 46 Plug reinforcement portion

[0059] 46a Circular inner circumference 46b Circular outer circumference

[0060] 47 Wave generator bearing DETAILED DESCRIPTION

[0061] Hereinafter, embodiments of a hollow type wave gear device according to an embodiment of the present invention will be described with reference to the drawings.

[0062] Figure 1 (a) is a schematic longitudinal sectional view showing a hollow type wave gear device according to an embodiment, Figure 1 (b) is a schematic transverse cross-sectional view thereof. The hollow type wave gear device 1 comprises a rigid internal gear 2 formed in a circular ring shape. On the inner side of the internal gear 2, a flexible external gear 3 formed in a top hat shape is coaxially arranged. The external teeth 3a of the external gear 3 can mesh with the internal teeth 2a of the internal gear 2. The internal gear 2 and the external gear 3 are maintained in a state of free relative rotation by means of bearings, in this case, cross roller bearings 4. On the inner side of the external gear 3, a wave generator 5 is coaxially arranged. The hollow rotating shaft 6 (hollow input shaft) passes through the center part of the wave generator 5 in a coaxial state. The hollow portion of the hollow rotating shaft 6 is a device hollow portion 7 extending in the direction of the center axis 1a.

[0063] In the hollow wave gear device 1, the external gear 3 is bent and deformed into an elliptical shape by the wave generator 5, and the external gear 3 meshes with the internal gear 2 at both ends of its major axis L1. When the wave generator 5 is rotated by the rotational force transmitted through the hollow rotating shaft 6, the meshing position of the two gears 2 and 3 moves in the circumferential direction, and a relative rotation corresponding to the difference in the number of teeth of the two gears 2 and 3 is generated between the two gears 2 and 3. If the internal gear 2 is fixed, the reduced rotation is output from the external gear 3.

[0064] The structure of each part is described below. The internal gear 2 is coaxially and tightly fixed to the end face of the inner ring 4a of the cross roller bearing 4 by bolts not shown. The external gear 3 includes: a cylindrical portion 3b that can be bent in the radial direction, a diaphragm 3c extending from one end of the cylindrical portion 3b toward the outside in the radial direction, and a rigid boss 3d in the shape of an annulus formed integrally on the outer peripheral edge of the diaphragm 3c. External teeth 3a are formed on the outer peripheral surface portion of the other end of the cylindrical portion 3b. The cross roller bearing 4 is arranged between the boss 3d and the internal gear 2. The boss 3d of the external gear 3 is coaxially and tightly fixed to the outer ring 4b of the cross roller bearing 4 by bolts not shown.

[0065] The wave generator 5 includes a rigid wave generator plug 5a and a wave generator bearing 5b. The outer peripheral surface of the wave generator plug 5a is formed as an elliptical outer peripheral surface 5c. The wave generator bearing 5b is mounted between the elliptical outer peripheral surface 5c and the inner peripheral surface of the cylindrical portion 3b of the external gear 3. In addition, a plug reinforcement portion 5d is provided on the wave generator 5 to improve the rigidity of the wave generator plug 5a.

[0066] The hollow rotating shaft 6 penetrates the central part of the wave generator 5 and extends toward both sides in the direction of the central axis 1a. A rotating shaft (not shown) such as a motor rotating shaft is coaxially connected and fixed to one shaft end 6a of the hollow rotating shaft 6. In this example, the hollow rotating shaft 6 is integrally formed with a plug shaft portion that defines the wave generator plug 5a and a plug reinforcement shaft portion that defines the plug reinforcement portion 5d.

[0067] The hollow rotating shaft 6 has a circular inner peripheral surface 6e having substantially the same inner diameter from the shaft end 6a on the input side to the shaft end 6d on the opposite side, and the device hollow portion 7 is defined by the circular inner peripheral surface 6e. The hollow rotating shaft 6 has a wave generator plug 5a and a plug reinforcement portion 5d integrally formed in the shaft portion from the shaft end 6a on the input side toward the shaft end 6d on the opposite side. The shaft portion of the hollow rotating shaft 6 other than the shaft portion where the wave generator plug 5a and the plug reinforcement portion 5d are formed is constituted by a circular outer peripheral surface 6g having substantially the same outer diameter.

[0068] A plug reinforcement portion 5d is formed in the hollow rotating shaft 6 at a position adjacent to the wave generator plug 5a in the direction of the central axis 1a. The thickness of the plug reinforcement portion 5d in the radial direction is greater than the thickness of the wave generator plug 5a in the radial direction. Figure 1 (a) Figure 1(c) The plug reinforcement portion 5d, the wave generator plug 5a, and the outline shape of the hollow rotating shaft 6 other than the above-mentioned portions are explained. As shown in these figures, in this example, the plug reinforcement portion 5d has a circular outer peripheral surface 6f, and the outer diameter of the circular outer peripheral surface 6f is larger than the major diameter of the elliptical shape that defines the elliptical outer peripheral surface 5c of the wave generator plug 5a. In addition, the wave generator plug 5a is arranged inside the cylindrical portion 3b of the external gear 3 at a position corresponding to the external teeth 3a, and the plug reinforcement portion 5d is formed in a manner to be located inside the cylindrical portion 3b at a position adjacent to the wave generator plug 5a on the shaft end 6d side.

[0069] In the hollow wave gear device 1, a plug reinforcement portion 5d having a thickness thicker than the wave generator plug 5a is formed adjacent to the wave generator plug 5a in the hollow rotating shaft 6. The wave generator plug 5a is reinforced by the plug reinforcement portion 5d having high rigidity formed in a dot shape adjacent to the wave generator plug 5a. Even if the hollow rotating shaft 6 is made thinner in order to increase the diameter of the device hollow portion 7, the plug reinforcement portion 5d can prevent or suppress the rigidity of the wave generator plug 5a from decreasing. In addition, since the plug reinforcement portion 5d having a high thickness is formed in a dot shape adjacent to the wave generator plug 5a, the required rigidity can be given to the wave generator plug 5a, and the increase in weight and inertia of the hollow rotating shaft 6 can be suppressed to a minimum. Therefore, the reduction in ratcheting torque of the hollow wave gear device 1 can be suppressed.

[0070] In this example, the plug reinforcement portion 5d is a portion where a thickness projection is formed in a dot shape on the outer circumferential surface of the hollow rotating shaft 6, and the inner circumferential surface of the hollow rotating shaft 6 is formed as a circular inner circumferential surface 6e of the same diameter at each position in the direction of the central axis 1a. The thickness projection is formed on the circular outer circumferential surface side of the hollow rotating shaft 6 to form a thick plug reinforcement portion 5d, so that the device hollow portion 7 of the hollow rotating shaft 6 can be formed to have a larger inner diameter.

[0071] Furthermore, the thick plug reinforcement portion 5d is formed by utilizing the dead space formed between the inner circumference of the cylindrical portion 3b of the top-hat shaped external gear 3 and the outer circumference of the hollow rotating shaft 6. No design changes in the shape of other parts of the hollow wave gear device 1 are required.

[0072] Here, in the hollow rotating shaft 6, the thick plug reinforcement portion 5d formed in a dot shape adjacent to the wave generator plug 5a can be used as a counterweight for the wave generator plug 5a. In this case, for example, the circular outer peripheral surface 6f of the plug reinforcement portion 5d is formed as an elliptical outer peripheral surface having a phase difference of 90 degrees with respect to the elliptical outer peripheral surface 5c of the wave generator plug 5a with the central axis 1a as the center, so that the weight balance of the hollow rotating shaft 6 during the rotation is achieved between the wave generator plug 5a and the plug reinforcement portion 5d.

[0073] (Example of a hollow wave gear device equipped with a plug reinforcement portion)

[0074] Figure 2 (a) is a schematic longitudinal sectional view showing another example of a hollow type wave gear device having a plug reinforcement portion, Figure 2 (b) is a schematic transverse cross-sectional view thereof. The basic structure of the hollow type wave gear device 21 is the same as that of the hollow type wave gear device 1 of the above-mentioned embodiment, and therefore, the same reference numerals are given to corresponding parts and their description is omitted. The different parts are described below.

[0075] Even in the hollow wave gear device 21, the wave generator 25 includes a rigid wave generator plug 25a and a wave generator bearing 25b. The outer peripheral surface of the wave generator plug 25a is an elliptical outer peripheral surface 25c. The wave generator bearing 25b is mounted between the elliptical outer peripheral surface 25c and the inner peripheral surface of the cylindrical portion 3b of the external gear 3. In order to improve the rigidity of the wave generator plug 25a, the wave generator 25 is provided with a plug reinforcement portion 25d.

[0076] The wave generator plug 25a is integrally formed on the outer peripheral surface side of the hollow rotating shaft 26. That is, a portion of the circular outer peripheral surface 26f of the hollow rotating shaft 26 protrudes outward in the radial direction with a constant width to form an elliptical outer peripheral surface 25c. The plug reinforcement portion 25d is integrally formed on the inner peripheral surface side of the hollow rotating shaft 26. That is, in the shaft portion of the hollow rotating shaft 26 where the wave generator plug 25a is integrally formed, its circular inner peripheral surface 26e protrudes inward in the radial direction with a constant width over the entire circumference, thereby forming: the inner peripheral surface thickness convex portion, that is, the plug reinforcement portion 25d. The width of the plug reinforcement portion 25d in the direction of the central axis 21a is set to a size including the portion where the wave generator plug 25a is formed.

[0077] In the hollow type wave gear device 21, a plug reinforcement portion 25d defined by the inner circumferential surface thickness convex portion is formed on the shaft portion of the hollow rotating shaft 26 where the wave generator plug 25a is formed. The wave generator plug 25a is reinforced by the plug reinforcement portion 25d composed of the inner circumferential surface thickness convex portion formed in a dot shape on the inner circumferential surface of the hollow rotating shaft 26. When the hollow rotating shaft 26 is thinned as a whole to achieve weight reduction, the plug reinforcement portion 25d can prevent or suppress the rigidity of the wave generator plug 25a with a thin thickness from being reduced. In addition, since the plug reinforcement portion 25d is provided on a part of the hollow rotating shaft 26, the increase in weight and inertia of the hollow rotating shaft 26 can be suppressed to a minimum. Therefore, the reduction in ratchet torque of the hollow type wave gear device 1 can be suppressed in the case where the hollow rotating shaft 26 with the wave generator plug 25a formed integrally is thinned to achieve weight reduction.

[0078] (Other example of a hollow wave gear device having a plug reinforcement portion)

[0079] Figure 3 2 is a longitudinal sectional view showing another example of a hollow type wave gear device having a plug reinforcement portion. The basic structure of the hollow type wave gear device 31 is the same as that of the hollow type wave gear device 1 of the above-mentioned embodiment, so the same reference numerals are used for corresponding parts and their description is omitted. The different parts are described below.

[0080] In the hollow wave gear device 31, the wave generator 35 includes a wave generator plug 35a and a wave generator bearing 35b. The wave generator plug 35a is integrally formed with a portion of the hollow rotating shaft 36. An elliptical outer peripheral surface 35c is formed on the outer peripheral surface of the wave generator plug 35a. The wave generator bearing 35b is mounted between the elliptical outer peripheral surface 35c and the inner peripheral surface of the cylindrical portion 3b of the external gear 3. In addition, a plug reinforcement portion 35d for increasing the rigidity of the wave generator plug 35a is integrally formed with the hollow rotating shaft 36.

[0081] In detail, the hollow rotating shaft 36 of this example is formed by a wave generator plug 35a (plug cylindrical portion) having a small diameter cylindrical shape and a plug reinforcement portion 35d having a large diameter cylindrical shape connected to one side of the wave generator plug 35a in a coaxial state. An elliptical outer peripheral surface 35c having a constant width and protruding toward the outside is formed on the circular outer peripheral surface 35e of the wave generator plug 35a.

[0082] The plug reinforcement portion 35d connected to the end of the wave generator plug 35a extends from the wave generator plug 35a in the direction along the central axis 31a, and protrudes from the open end of the cylindrical portion 3b of the external gear 3 toward the outside of the cylindrical portion 3b, and is located adjacent to the wave generator bearing 35b in the direction of the central axis 31a. The plug reinforcement portion 35d has a thickness greater than that of the wave generator plug 35a, and the inner diameter of the circular inner peripheral surface 35f thereof is substantially the same as the outer diameter of the wave generator plug 35a. The annular end surface 35g of the wave generator plug 35a is located at the end of the circular inner peripheral surface 35f. The plug reinforcement portion 35d is formed as a shaft hole portion for inserting and fixing a rotating shaft such as a motor rotating shaft, and the inserted rotating shaft (not shown) abuts against the annular end surface 35g to be positioned in the axial direction.

[0083] In order to increase the inner diameter of the hollow portion of the hollow rotating shaft 36 integrally formed with the wave generator plug 35a, or to reduce the weight and inertia, the thickness of the hollow rotating shaft 36 may be reduced. If the hollow rotating shaft 36 is made thinner, the wave generator plug 35a also becomes thinner, and its rigidity is reduced. In this case, it may not be possible to ensure the rigidity required for the external gear 3 to bend and deform into an elliptical shape so as to reliably mesh with the internal gear 2.

[0084] In this example, a plug reinforcement portion 35d for reinforcing the wave generator plug 35a is formed on the hollow rotating shaft 36. The plug reinforcement portion 35d can increase the inner diameter of the device hollow portion 7 and provide the wave generator plug 35a with the required rigidity. Therefore, the hollow rotating shaft 36 formed with the wave generator plug 35a can be made lighter while ensuring its rigidity to prevent or suppress a decrease in ratchet torque.

[0085] (Example of a cup-type wave gear device equipped with a plug reinforcement portion)

[0086] Figure 4 (a) is a schematic longitudinal sectional view showing a cup-type wave gear device having a plug reinforcement portion, Figure 4(b) is a schematic transverse cross-sectional view thereof. The cup-type wave gear device 41 includes a cup-shaped flexible external gear 43 coaxially arranged inside a rigid internal gear 42. The external gear 43 includes a flexible cylindrical portion 43b formed with external teeth 43a that can mesh with the internal teeth 42a of the internal gear 42. A wave generator 44 is coaxially arranged inside the cylindrical portion 43b of the external gear 43. The wave generator 44 bends and deforms the cylindrical portion 43b of the external gear 43 into an elliptical shape, and partially meshes the external teeth 43a of the external gear 43 with the internal teeth 42a of the internal gear 42 at two locations at both ends of the major axis of the ellipse. When the wave generator 44 rotates, the meshing position of the external teeth 43a and the internal teeth 42a moves in the circumferential direction, and a relative rotation corresponding to the difference in the number of teeth of the two gears 42 and 43 is generated between the two gears 42 and 43.

[0087] The external gear 43 includes a diaphragm 43c extending radially from a first end of a cylindrical portion 43b and a rigid annular boss 43d formed on the inner periphery of the diaphragm 43c. External teeth 43a are formed on a second end of the cylindrical portion 43b.

[0088] The wave generator 44 includes a wave generator plug 45 having an elliptical outer peripheral surface 45 a , a plug reinforcement portion 46 provided to increase the rigidity of the wave generator plug 45 , and a wave generator bearing 47 mounted between the elliptical outer peripheral surface 45 a and the inner peripheral surface of the cylindrical portion 43 b of the external gear 43 .

[0089] The wave generator plug 45 includes a plug cylindrical portion 45b having an elliptical outer peripheral surface 45a, a disc-shaped rib 45c extending radially inward from the inner peripheral surface of the plug cylindrical portion 45b, and an inner cylindrical portion 45d formed coaxially with the center portion of the rib 45c. The inner cylindrical portion 45d is formed with an axial hole 45e extending through the inner cylindrical portion 45d.

[0090] The plug reinforcement portion 46 is an annular portion formed in a continuous manner with the end portion of the external gear 43 of the plug cylindrical portion 45b on the diaphragm 43c side. The thickness of the plug reinforcement portion 46 in the radial direction is thicker than the thickness of the plug cylindrical portion 45b. In this example, the plug reinforcement portion 46 has a circular inner peripheral surface 46a having the same diameter as the diameter of the plug cylindrical portion 45b. In addition, the plug reinforcement portion 46 has a circular outer peripheral surface 46b having an outer diameter larger than the outer diameter of the major axis of the elliptical shape defining the elliptical outer peripheral surface 45a of the plug cylindrical portion 45b.

[0091] Furthermore, the plug reinforcement portion 46 can be used as a counterweight for the wave generator plug 45. In this case, for example, the outer peripheral surface of the plug reinforcement portion 46 is not formed as a circular outer peripheral surface, but is formed as an elliptical outer peripheral surface having a phase difference of 90 degrees with respect to the elliptical outer peripheral surface 45a of the wave generator plug 45, with the central axis 41a as the center.

[0092] In order to reduce the weight and inertia of the wave generator plug 45, the thickness of the plug cylindrical portion 45b, the rib portion 45c and the like, which are the components thereof, may be reduced. If the thickness of the above portions is set to be thin, the rigidity of the wave generator plug 45 will be reduced, and sometimes it may not be possible to ensure the rigidity required for the external gear 43 to be bent and deformed into an elliptical shape and reliably mesh with the internal gear 42. In this example, in order to reinforce the wave generator plug 45, the end of the plug cylindrical portion 45b is extended in the direction of the central axis 41a, and the extended portion is formed as a thick plug reinforcement portion 46. The plug reinforcement portion 46 provides the wave generator plug 45 with the required rigidity. By minimizing the increase in weight and inertia of the plug reinforcement portion 46, the wave generator plug 45 can be reduced in weight, and at the same time, its rigidity can be ensured to prevent or suppress the reduction of the ratchet torque.

Claims

1. A hollow wave gear device, comprising: Rigid internal gears; an external gear coaxially disposed inside the internal gear and having a flexible cylindrical portion formed with external teeth capable of meshing with the internal teeth of the internal gear; a wave generator coaxially disposed inside the cylindrical portion of the external gear, causing the cylindrical portion to bend and deform into an elliptical shape and partially mesh with the inner teeth of the internal gear at two locations in the circumferential direction, and once driven to rotate, causing the meshing position between the external teeth and the internal teeth to move in the circumferential direction; as well as A hollow rotating shaft coaxially passes through the wave generator and extends therefrom. The hollow wave gear device is characterized in that: The wave generator has: A wave generator plug having an elliptical outer peripheral surface; a plug reinforcement portion provided to increase the rigidity of the wave generator plug; and a wave generator bearing mounted between the elliptical outer peripheral surface and the inner peripheral surface of the cylindrical portion of the external gear, The hollow rotating shaft is integrally formed with a first shaft portion defining the wave generator plug and a second shaft portion defining the plug reinforcement portion. In the hollow rotating shaft, the plug reinforcement portion is formed at a position adjacent to the wave generator plug in the direction of the central axis of the hollow rotating shaft, The thickness of the plug reinforcement portion in the radial direction is greater than the thickness of the wave generator plug in the radial direction. The inner circumferential surfaces of the wave generator plug and the plug reinforcement portion are formed as circular inner circumferential surfaces with the same diameter at each position in the direction of the central axis. The outer peripheral surface of the plug reinforcement portion has, at each position in the direction of the central axis, an outer diameter larger than the major diameter of the elliptical shape defining the elliptical outer peripheral surface of the wave generator plug, The outer peripheral surface of the plug reinforcement portion is an elliptical outer peripheral surface having a phase difference of 90 degrees with respect to the elliptical outer peripheral surface of the wave generator plug, with the central axis as the center.

2. The hollow wave gear device according to claim 1, characterized in that: The external gear is a cup-shaped or top-hat-shaped external gear. The external gear includes: a diaphragm extending in a radial direction from a first end of one side of the cylindrical portion, and a rigid annular boss formed on an outer peripheral edge or an inner peripheral edge of the diaphragm. The external teeth are formed at a second end portion of the other side of the cylindrical portion. The wave generator plug is arranged inside the cylindrical portion at a position corresponding to the external teeth, The plug reinforcement portion is disposed inside the cylindrical portion at a position adjacent to the wave generator plug on the first end side.

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