Strain wave gear device

Abstract

A strain wave gear device (4) is provided with: a device case (41); an internally toothed gear (42); and an annular gap portion (47) which is formed between the external gear (43) and the main bearing (46), surrounds the cylindrical portion (43a) of the external gear (43), and in which a gap filling ring (48) made of a lightweight resin material is fitted in order to fill the gap portion (47). As a result, the contour shape of the gap-filling ring (48) is appropriately set, and by forming the gap-filling ring (48) from a material having a small weight per volume, a gap portion (47) formed on the outer peripheral side of the externally toothed gear (43) can be filled without causing an unnecessary increase in mass, and without causing unnecessary retention of a lubricant.

Description

TECHNICAL FIELD

[0001] The present application relates to a wave gear device, and more particularly to a wave gear device which does not cause an increase in weight and which cannot form a lubricant accumulation portion that causes retention of lubricant on the outer peripheral side of a flexible outer tooth gear. BACKGROUND

[0002] As for a wave gear device that is generally used as a speed reducer, there is a unit type wave gear device in which a rigid inner tooth gear and a flexible outer tooth gear are assembled in a state in which they can relatively rotate by means of a main bearing inside a device housing. This type of wave gear device is described in Patent Documents 1 and 2.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT DOCUMENTS

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-206265

[0006] Patent Document 2: Japanese Patent Application Publication No. 2022-10593 SUMMARY

[0007] As for the unit type wave gear device, the inner tooth gear and the bearing are disposed on the outer peripheral side of the outer tooth gear with a prescribed interval in the axial direction inside the device housing. An annular gap that surrounds the outer tooth gear is formed between the inner tooth gear and the main bearing. This annular gap communicates with the meshing portions of the inner tooth gear and the outer tooth gear. Each portion in the circumferential direction of the outer tooth gear repeatedly flexes in the radial direction, and thus a meshing state in which the inner tooth gear meshes with the outer tooth gear and a meshing release state in which the meshing is released repeatedly occur. The lubricant such as grease that is applied or filled to the meshing portions flows out to the gap by this action. The gap can become a lubricant accumulation portion in which the flowed-out lubricant is retained. If the volume of this gap is large, the lubricant is unnecessarily retained, and there is a risk that the lubrication of the meshing portions and the like cannot be properly performed.

[0008] Therefore, in order to not form a large gap, it is necessary to form a portion of a member that surrounds the gap, such as a portion of the device housing made of aluminum, a portion of the inner tooth gear made of cast iron, and the like, in a shape that protrudes in the axial direction, and thus a large gap cannot be formed. However, filling the gap with a metal member causes an increase in mass, and thus the marketability of the product is reduced.

[0009] In view of the above-described problems, an object of the present application is to provide a wave gear device that is configured so as not to cause an increase in mass and so as not to form a large gap that becomes a lubricant accumulation portion on the outer peripheral side of an outer tooth gear.

[0010] The wave gear device of the present application is characterized by comprising:

[0011] apparatus housing;

[0012] a rigid internally toothed gear mounted to the apparatus housing;

[0013] a flexible externally toothed gear disposed inside the apparatus housing and the internally toothed gear;

[0014] a wave generator that causes the externally toothed gear to flex in a radial direction to partially mesh with the internally toothed gear;

[0015] a main bearing fitted between the apparatus housing and the externally toothed gear to support the externally toothed gear in a state in which it can rotate relative to the apparatus housing;

[0016] an annular gap portion formed between the apparatus housing, the internally toothed gear, the externally toothed gear, and the main bearing to surround the externally toothed gear; and

[0017] a gap filling member inserted into the gap portion to fill the gap portion and mounted to at least one of the apparatus housing and the internally toothed gear,

[0018] the gap filling member is formed of a non-permeable material that does not allow a lubricant applied or supplied to a meshing portion of the internally toothed gear and the externally toothed gear and a sliding portion of the main bearing to pass through.

[0019] the gap filling member is formed of a lightweight material such as a resin that has a smaller weight per unit volume than the materials of the apparatus housing and the internally toothed gear. In addition, in order to further reduce the mass, a hollow member or a member provided with a hollow portion can be used as the gap filling member.

[0020] Effects of the Invention

[0021] In the present invention, the annular gap portion that surrounds the externally toothed gear is fitted with a gap filling member formed of a non-permeable material that does not allow a lubricant to pass through. The profile shape of the gap filling member is appropriately set, and in addition, by forming the gap filling member of a material that has a smaller weight per unit volume, the gap portion can be filled without causing unnecessary increase in mass, and unnecessary retention of the lubricant can be prevented. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic longitudinal sectional view showing a rotary actuator according to an embodiment of the present invention.

[0023] Figure 2 is an explanatory diagram showing another example of a gap filling ring as a gap filling member. DETAILED DESCRIPTION

[0024] Embodiments of the present application will be described below with reference to the accompanying drawings. The embodiments described below show one example of the present application, and are not intended to limit the present application to the structures of the embodiments.

[0025] Figure 1 is a schematic longitudinal sectional view showing a rotary actuator according to an embodiment of the present application. The rotary actuator 1 is configured to include a cylindrical actuator housing 2, and a motor 3 and a wave gear device 4 assembled inside thereof. An encoder housing 5 is mounted to an end portion of the actuator housing 2 on the motor side, and a motor encoder 6 (shown by a box of broken lines in the drawing) is assembled inside thereof. The motor 3 is of a general structure, and includes a motor shaft 31, a motor rotor 32 mounted to the motor shaft 31, and a motor stator 33 mounted to an inner peripheral surface portion of the actuator housing 2 on the motor side.

[0026] The wave gear device 4 includes a device housing 41 formed as a part of the actuator housing 2, a rigid internal gear 42 mounted to the device housing 41, a flexible external gear 43 coaxially arranged inside the internal gear, a wave generator 44 embedded inside the external gear 43, and an input shaft 45 coaxially mounted to the wave generator 44. The input shaft 45 is integrated with the motor shaft 31 in this example. The external gear 43 is supported by the device housing 41 in a rotatable state by means of a main bearing 46. Further, an annular gap portion 47 surrounding the external gear 43 is formed between the device housing 41, the internal gear 42, the external gear 43, and the main bearing 46. A gap filling ring 48 (gap filling member) is fitted in the gap portion 47 in order to substantially fill the gap portion 47.

[0027] Further description will be given. The cylindrical device housing 41 is formed with an inner peripheral surface portion 41a for internal gear mounting having the smallest diameter, an inner peripheral surface portion 41b for gap formation having a larger inner diameter than the inner peripheral surface portion 41a, and an inner peripheral surface portion 41c for main bearing mounting having a larger inner diameter than the inner peripheral surface portion 41b, from the motor 3 side in the axial direction.

[0028] The internal gear 42 of this example is a circular ring-shaped member formed in a rectangular cross section, and its outer peripheral surface portion is joined to the inner peripheral surface portion 41a of the device housing 41 by cast joining, thereby achieving integration with the device housing 41, and an internal gear 42a is formed in the circular inner peripheral surface of the internal gear 42. In addition, a disc-shaped partition plate 42b that partitions the internal space of the wobble gear device 4 and the internal space of the motor 3 is integrally formed in the internal gear 42. The partition plate 42b extends from the motor side end surface of the internal gear 42, and a bearing holder 42c that extends toward the motor side is formed in the inner peripheral edge portion thereof. The shaft portion of an input shaft 45 that extends toward the motor side from a wobble generator 44 is supported by a bearing 7 that is fitted to the bearing holder 42c.

[0029] The external gear 43 is formed in a cup shape, and has a cylindrical portion 43a that can be flexed in the radial direction, an external gear 43b that is formed in the outer peripheral surface portion on the side of the open end that is one end portion of the cylindrical portion 43a, a diaphragm 43c that extends toward the inside in the radial direction from the other end portion of the cylindrical portion 43a, and a rigid boss 43d that is formed in a circular ring shape in conjunction with the inner peripheral edge of the diaphragm 43c. In the inside of the cylindrical portion 43a, a cylindrical bearing holder 8 is mounted to the boss 43d, and the shaft portion of the input shaft 45 that extends toward the opposite side of the motor from the wobble generator 44 is supported by a bearing 9 that is fitted to the bearing holder 8.

[0030] The wobble generator 44 has an elliptical profile cam plate 44a that is integrated with the input shaft 45, and a wobble generator bearing 44b that is fitted to the elliptical outer peripheral surface of the cam plate 44a. The portion of the external gear 43 in which the external gear 43b is formed is flexed into an elliptical shape by the wobble generator 44, and the external gears 43b at both ends of the major axis of the elliptical shape engage with the internal gear 42a. If the cam plate 44a of the wobble generator 44 is rotated, the engagement positions of the two gears move in the circumferential direction, and a relative rotation corresponding to the difference in the number of teeth of the two gears is generated between the two gears. In this example, the internal gear 42 is a fixed side member that is mounted to the device housing 41, and the external gear 43 rotates. The rotation of the external gear 43 is output as a reduced rotation to a load side that is not shown.

[0031] The main bearing 46 has an outer race 46a that is mounted to the inner peripheral surface portion 41c of the device housing 41, an inner race 46b that is mounted to the boss 43d of the external gear 43, and a plurality of rolling elements 46c that are fitted between the above-mentioned members.

[0032] The gap portion 47 is formed between the inner gear 42 and the main bearing 46, which are opposed in the axial direction, between the cylindrical portion 43a of the outer gear 43 and the inner peripheral surface portion 41b of the device housing 41 that surrounds the cylindrical portion 43a. The gap portion 47 communicates with the meshing portion 40 of the inner gear 42 and the outer gear 43, and with the track portion of the rolling element 46c formed between the outer ring 46a and the inner ring 46b of the main bearing 46.

[0033] The gap filling ring 48 that is fitted to the gap portion 47 is formed of a lightweight material that is lighter than any of the materials of the device housing 41, the inner gear 42, and the main bearing 46, on a unit volume weight basis. In this example, a resin ring formed in a rectangular cross section is used. The gap filling ring 48 is a non-permeable ring that does not allow lubricant applied or supplied to the meshing portion 40 of the inner gear 42 and the outer gear 43, and the sliding portion (inside of the track portion) of the main bearing 46 to pass through. Therefore, the gap filling ring 48 does not absorb the lubricant. In addition, the gap filling ring 48 is fixed to the inner peripheral surface portion 41b of the device housing 41 with an adhesive or the like. A fixing means other than an adhesive can also be used. In addition, the gap filling ring 48 is arranged so as to form a prescribed gap with the outer peripheral surface of the cylindrical portion 43a in a manner that does not interfere with the cylindrical portion 43a that is deflected in the radial direction. In the case of being arranged in a state of being in contact with the cylindrical portion 43a or in a case where contact is possible, it is sufficient that the gap filling ring 48 is formed of a material that is deformed by deflection in accordance with the deflection of the cylindrical portion 43a.

[0034] If the motor 3 drives the wave gear device 4, the meshing position of the outer gear 43 relative to the inner gear 42 moves in the circumferential direction in accordance with the rotation of the wave generator 44, and a reduced rotation corresponding to the difference in the number of teeth of the two gears 42, 43 is extracted from the outer gear 43. The reduced rotation of the outer gear 43 is output to the load side that is not shown from the inner ring 46b of the main bearing 46 that functions as an output shaft.

[0035] In the driven state of the wave gear device 4, lubricant circulates in the gap portion 47. The gap portion 47 is filled in by the gap filling ring 48 that is substantially composed of a lightweight material. Thus, it is possible to avoid the disadvantage that lubricant remains in the gap portion 47 and lubrication of the lubrication target portion such as the meshing portion is not properly performed. In addition, the gap filling ring 48 is a lightweight resin member, and therefore, unlike the case where the inner peripheral surface portion 41b of the device housing 41 is extended inward to form a large volume gap portion 47, does not result in an increase in mass.

[0036] Further, the shape and volume of the gap portion 47 vary depending on the mechanical characteristics, shape, layout, and the like required for the external gear 43, the main bearing 46, and the like. For example, the width dimension in the axial direction of the gap, the height dimension in the radial direction vary depending on the axial length of the cylindrical portion 43a of the external gear 43, the tooth width of the external teeth, the size of the main bearing, the arrangement position in the axial direction. Accordingly, as long as the shape and material of the gap filling member 48 for filling the gap portion 47 are appropriately set.

[0037] Further, in the present example, a solid member formed in a rectangular shape is used as the gap filling ring 48. In order to achieve weight reduction of the gap filling member 48, a hollow member or a member provided with a hollow portion can also be used. For example, as shown in FIG. 8, a hollow ring 48A made of resin formed in a rectangular cylindrical cross section can be used as the gap filling ring 48. Figure 2

[0038] Further, in the present example, a single gap filling ring 48 is arranged. Two or more gap filling rings of the same shape or different shapes can also be assembled depending on the situation.​

Claims

1. A wave gear device, characterized in that, The wave gear device includes: Device housing; A rigid internal gear, which is mounted on the housing of the device; A flexible external gear is disposed inside the device housing and the internal gear; A wave generator that causes the external gear to flex radially and partially mesh with the internal gear; A main bearing is assembled between the device housing and the external gear, supporting the external gear in a state that allows it to rotate relative to the device housing; An annular gap portion is formed between the device housing, the internal gear, the external gear, and the main bearing, surrounding the external gear; as well as A gap-filling component, inserted into the gap portion to fill it, is mounted on at least one of the device housing and the internal gear. The gap-filling component is formed of an impermeable material that prevents lubricant applied to or supplied to the meshing portions of the internal and external gears and the sliding portions of the main bearing from passing through.

2. The wave gear device according to claim 1, characterized in that, The gap-filling component is made of a lightweight material with a unit volume weight that is smaller than that of the device housing and the internal gear.

3. The wave gear device according to claim 1, characterized in that, The gap-filling component is a hollow component or a component with a hollow portion.

4. The wave gear device according to claim 1, characterized in that, The gap-filling component is formed of resin material.

5. The wave gear device according to claim 1, characterized in that, The gap-filling component has flexibility that allows it to flex in the radial direction of the external gear.

6. The wave gear device according to any one of claims 3 to 5, characterized in that, The external gear comprises: a cylindrical portion capable of flexing in the radial direction; external teeth formed on the outer peripheral surface of the cylindrical portion; a diaphragm extending radially inward from one end of the cylindrical portion; and a rigid boss formed on the inner peripheral edge of the diaphragm. The internal gear is an integral housing component that is joined to the inner circumferential side of the device housing by casting. The main bearing comprises: an outer ring mounted on the device housing; and an inner ring mounted on the boss of the external gear. The clearance portion is formed between the cylindrical portion of the external gear and the inner circumferential surface portion of the housing surrounding the cylindrical portion, between the internal gear and the main bearing, which are opposed in the axial direction. The gap-filling component is installed on at least one of the device housing and the internal gear, and is formed of a lightweight material with a unit volume weight smaller than that of any of the devices housing, the internal gear, and the main bearing.

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