Strain wave gearing

Abstract

The harmonic gear device (1) is a harmonic generator (4) with a hollow input shaft (5) and an external gear (3) bent in the radial direction to mesh with an internal gear (2). The harmonic generator (4) is a wave bearing (43) with a ball retainer (47). The outer circumferential surface of the input shaft located inside the external gear (3) on the hollow input shaft (5) is covered by an oil-dispensing film (14). The surface of the ball retainer (47) is also covered by an oil-dispensing film (15). By means of the oil-dispensing films (14, 15), the grease stirring resistance of the hollow input shaft (5) and the ball retainer (47) is reduced, thereby reducing the torque loss of the harmonic gear device (1).

Description

Technical Field

[0001] The present invention relates to a wave gear device having an input shaft. Prior Art

[0002] Harmonic wave gearing is widely used as a speed reducer. It is known to have an input shaft that transmits high-speed rotation from a motor or other device to a harmonic generator. Reducing torque loss is one of the requirements for harmonic wave gearing. During operation, torque loss occurs due to frictional resistance in the meshing gears, rotational resistance in the bearings, and stirring resistance of the grease (lubricant). This causes some of the energy from the input shaft's rotation to be converted into heat. Reducing this loss can achieve advantages such as reduced heat generation and a lower drive motor capacity.

[0003] Because grease's stirring resistance increases with higher stirring speeds, the stirring resistance near the input shaft of a wave gear system operating at several thousand rpm accounts for a significant portion of the total torque loss. Furthermore, since a large amount of grease is applied near the input shaft and wave bearings to maintain long-term lubricity, contact between the grease and the input shaft occurs not only near the wave bearing balls, but also contributes to increased stirring resistance.

[0004] To reduce stirring resistance, lowering the viscosity of the grease base oil and reducing the amount of coating can be considered. However, both methods involve a trade-off in lubricity, and further improvement is difficult given the balanced design of existing products that consider torque loss and lubricity.

[0005] Furthermore, in a wave gear device, in order to reduce the outflow of lubricant from the meshing portion between the internal gear and the external gear, it has been proposed to form an oil repelling portion on the surface of the body portion of the external gear, which has a higher oil repellency than the surface of the teeth of the external gear (Patent Document 1). [Prior Art Literature] [Patent Document]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-53912 Summary of the Invention

[0007] [Problems to be solved by the invention]

[0008] In a wave gear unit, the grease near the input shaft and the balls of the wave bearings comes into contact with or adheres to the input shaft, the retainer of the wave bearings, etc. This contact with the grease increases stirring resistance, which in turn increases torque loss in the wave gear unit.

[0009] The object of the present invention is to provide a harmonic gear device capable of suppressing an increase in torque loss caused by an increase in stirring resistance near an input shaft and a wave bearing caused by a lubricant. [Methods used to solve the problem]

[0010] The harmonic gear device of the present invention comprises: Rigid inner gear; The flexible outer gear is coaxially arranged inside the inner gear; A harmonic generator comprising a wave plug and a wave bearing, wherein the wave bearing is mounted between the non-circular outer peripheral surface of the wave plug and the inner peripheral surface of the external gear; An input shaft is coaxially mounted to the aforementioned wave plug; The outer peripheral surface portion of the input shaft is located inside the aforementioned external gear on the aforementioned input shaft; and The first oil-repellent film, such as a fluororesin film, covers the outer peripheral surface of the input shaft and has oil-repellent properties for the lubricant applied or supplied to the wave bearing.

[0011] Furthermore, in the harmonic gear device of the present invention, The aforementioned wave bearing has: Inner and outer wheels; A plurality of rotating bodies are rotatably inserted into an annular track groove formed between the inner wheel and the outer wheel; A retainer, which holds the rotating body at positions spaced apart at predetermined intervals in the circumferential direction; and A second oil-repellent film such as a fluororesin film covers the surface of the retainer and has oil-repellent properties to the lubricant. [Effects of the Invention]

[0012] In the harmonic gear device of the present invention, the following effects can be obtained, thereby reducing the torque loss of the harmonic gear device. (1) Reduction of lubricant adhesion: Through the oil-peeling film, the lubricant is easily thrown away by centrifugal force, the lubricant adhesion is reduced, and the stirring resistance will become smaller. (2) Reduction of lubricant shear rate: By removing the oil film, sliding occurs between the surface in contact with the lubricant and the lubricant, and the lubricant shear rate is reduced, thereby reducing the stirring resistance. Simple diagram description

[0013] FIG1 is a schematic longitudinal sectional view of a wave gear device according to an embodiment of the present invention. FIG. 2 is an explanatory diagram showing a grease lubricated portion of the wave gear device of FIG. 1 . Implementation Method

[0014] A wave gear device according to an embodiment of the present invention will be described below with reference to Figures 1 and 2. The wave gear device 1 comprises a rigid internal gear 2, a flexible silk hat-shaped external gear 3, a harmonic generator 4, a hollow input shaft 5, and a main bearing 6 composed of a cross roller bearing, which supports the external gear 3 for free rotation relative to the internal gear 2. Furthermore, the wave gear device 1 comprises a fixed-side end plate 7 integrally formed with the internal gear 2, and an output-side end plate 8, which serves as an output shaft and is coaxially fixedly connected to the external gear 3. One end 51 of the hollow input shaft 5 is rotatably supported by the fixed-side end plate 7 via a bearing 9a, while the other end 52 of the hollow input shaft 5 is rotatably supported by the output-side end plate 8 via a bearing 9b.

[0015] The internal gear 2 is annular in shape, with internal teeth 21 formed on its circular inner circumference. A fixed-side end plate 7 is integrally formed on the end surface of the internal gear 2, located on the axial end portion 51 thereof. An inner ring 61 of the main bearing 6 is coaxially secured to the other axial side of the internal gear 2.

[0016] The external gear 3 comprises a cylindrical body 32 with external teeth 31 formed thereon, a diaphragm 33 that widens radially outward from the end of the cylindrical body 32, and an annular boss 34 integrally formed with the outer circumference of the diaphragm 33. The cylindrical body 32 is coaxially positioned within the internal gear 2 and the inner race 61 of the main bearing 6, with the external teeth 31 facing and meshing with the internal teeth 21. The boss 34 is axially located between the outer race 62 of the main bearing 6 and the output-side end plate 8. The outer race 62, boss 34, and output-side end plate 8 are coaxially fastened and fixed together.

[0017] The harmonic generator 4 comprises a wave plug 42 and a wave bearing 43. The wave plug 42 has an elliptical outer surface 41 of a certain width, integrally formed with the outer circumference of the hollow input shaft 5. The wave bearing 43 is mounted between the elliptical outer surface 41 of the wave plug 42 and the inner circumference 35 of the cylindrical body 32, which is formed with the external teeth 31 of the external gear 3. The wave bearing 43 comprises a flexible inner race 44, a flexible outer race 45, a plurality of balls 46, and an annular ball retainer 47. The balls 46 are rotatably inserted between the inner and outer races, and the ball retainer 47 retains the balls 46 at regular intervals in the circumferential direction.

[0018] Inside the wave gearing device 1, an outer peripheral gap 11 is formed on the outside of the external gear 3, surrounded by the inner ring 61 of the main bearing 6, the external gear 3, and the internal gear 2. This outer peripheral gap 11 extends along the outer circumference of the cylindrical body 32 of the external gear 3 and meshes with the meshing portion between the internal teeth 21 and the external teeth 31. Furthermore, an inner peripheral gap 12 is formed on the inside of the external gear 3, surrounded by the external gear 3, the hollow input shaft 5, the stationary end plate 7, and the output end plate 8. The wave bearing 43 is located within this inner peripheral gap 12.

[0019] Lubricant is applied or supplied to lubricated areas within the wave gear device 1. These areas are primarily the meshing area between the internal teeth 21 and external teeth 31, the wave bearing 43 of the harmonic generator 4, and the sliding area between the outer race 45 of the wave bearing 43 and the inner circumferential surface of the external gear 3. For example, as indicated by the textured area G in Figure 2, grease is applied or filled inside and around the wave bearing 43 within the inner circumferential gap 12.

[0020] As previously mentioned, the stirring resistance of grease increases with higher stirring speeds. Therefore, the stirring resistance near the hollow input shaft 5, used at high speeds of several thousand rpm, accounts for a significant proportion of the total torque loss in the wave gear device 1. Furthermore, to maintain lubricity over a long period of time, a large amount of grease is applied to the hollow input shaft 5 and near the wave bearing 43. Consequently, grease contacts not only the area near the balls 46 of the wave bearing 43 but also the hollow input shaft 5, contributing to the increased stirring resistance.

[0021] To prevent such defects, in the wave gear device 1, the outer circumference of the input shaft, located inside the external gear 3 of the hollow input shaft 5, is covered with an oil-repellent coating, such as a fluorine coating, that has grease-repellent properties. In this example, as shown in Figure 2, the outer circumferences 53 and 56 of the input shaft on either side of the wave plug 42 and the end surfaces 54 and 55 on either side of the wave plug 42 are covered with an oil-repellent coating 14. Furthermore, in this example, the entire surface of the ball retainer 47 of the wave bearing 43 is also covered with an oil-repellent coating 15, such as a fluorine coating. The oil-repellent coatings 14 and 15 can be the same type of coating. Alternatively, they can be different types. Furthermore, the coatings 14 and 15 can have the same or different thicknesses. The oil repellent films 14 and 15 are formed with appropriate materials and thicknesses according to the material of the hollow input shaft 5 , the material of the ball retainer 47 , the type of grease used, and the like.

[0022] In the harmonic gear device 1, the elliptical harmonic generator 4 is embedded within the internal external gear 3. The portion of the external teeth 31 formed therein is bent into an elliptical shape, and the portion of the external teeth 31 located at or near the major axis of the ellipse meshes with the internal teeth 21. A hollow input shaft 5 is connected to the output shaft of a motor (not shown) and is driven at high speed. As the wave plug 42 of the harmonic generator 4 rotates integrally with the hollow input shaft 5 at high speed, the meshing position of the external gear 3 relative to the internal gear 2 moves circumferentially. The number of teeth on the internal gear 2 is 2n greater than that on the external gear 3 (n: a positive integer). Relative rotation occurs between the two gears 2 and 3 in accordance with this tooth number difference. The internal gear 2 is the stationary side, and the input rotation is significantly reduced from the external gear 3 via the output-side end plate 8 and then extracted to the load side (not shown).

[0023] Here, the outer circumferences 53 and 56 of the hollow input shaft 5, which rotates at high speed, and the end surfaces 54 and 55 on both sides of the wave plug 42 are covered with the oil-repellent coating 14. Furthermore, the surface of the ball retainer 47, which rotates at a predetermined speed along with the balls 46 as the hollow input shaft 5 rotates at high speed, is also covered with the oil-repellent coating 15. When the hollow input shaft 5 rotates at high speed, the grease is easily removed by centrifugal force through the oil-repellent coating 14, reducing the amount of grease adhering to the hollow input shaft 5 and the resulting grease agitation resistance. Similarly, the grease in the ball retainer 47, which rotates at a predetermined speed, is easily removed by centrifugal force through the oil-repellent coating 15, reducing the amount of grease adhering to the ball retainer 47. This reduced grease adhering to the ball retainer 47 reduces the grease agitation resistance acting on the hollow input shaft 5 and the ball retainer 47.

[0024] Furthermore, the oil-repellent coating 14 causes sliding movement between the grease and the grease-contacting input shaft outer circumference portions 53 and 56 of the hollow input shaft 5 and the end surfaces 54 and 55 on both sides of the wave plug 42. This reduces the grease shear velocity, thereby reducing the grease stirring resistance acting on the hollow input shaft 5. Similarly, the oil-repellent coating 15 causes sliding movement between the grease and the grease-contacting surface of the ball retainer 47. This reduces the grease shear velocity, thereby reducing the grease stirring resistance acting on the ball retainer 47.

[0025] In this manner, the oil-repellent films 14 and 15 can reduce the grease stirring resistance acting on the hollow input shaft 5 and the ball retainer 47 , thereby reducing the torque loss of the wave gear device 1 .

[0026] (Other embodiments) In the above embodiment, the present invention is applied to a top-hat-type harmonic gearing device having a top-hat-shaped external gear. The present invention is also applicable to other types of harmonic gearing devices. For example, it can be applied to a cup-type harmonic gearing device having a cup-shaped external gear, or to a flat-type harmonic gearing device having a driving-side internal gear, a stationary-side internal gear, and a cylindrical external gear.

[0027] 1: Harmonic gear device 2: Internal gear 3: External gear 4: Harmonic Generator 5: Hollow input shaft 6: Main bearing 7:Fix the side end plate 8: Output side end plate 9a,9b: Bearings 11: Outer peripheral side gap part 12: Inner circumference clearance 14,15: Oil-repellent film 21: Internal teeth 31: External teeth 32:Tubular body part 33: Diaphragm 34: bulge 35: Inner circumference 41: Elliptical outer surface 42: Wave thrombosis 43: Wave bearing 44: Inner wheel 45: Outer wheel 46: Ball 47: Ball retainer 51,52: shaft end 54,55: End face 56: Input shaft outer surface 61: Inner wheel 62: Outer wheel G: Textured part

Claims

1. A harmonic gear device comprising: a rigid inner gear; a flexible outer gear coaxially disposed inside the inner gear; a harmonic generator having a wave plug and a wave bearing, the wave bearing being mounted between a non-circular outer peripheral surface of the wave plug and an inner peripheral surface of the outer gear; an input shaft coaxially mounted to the wave plug; an outer peripheral surface portion of the input shaft located inside the outer gear on the input shaft; and a first oil-repellent film covering the outer peripheral surface portion of the input shaft and having oil-repellent properties for lubricants applied to or supplied to the wave bearing.

2. The harmonic gear device as described in claim 1, wherein, The aforementioned wave bearing comprises: an inner wheel and an outer wheel; and a plurality of rotating bodies that are rotatably inserted into an annular track groove formed between the inner wheel and the outer wheel. A retainer holds the aforementioned rotating body at a certain interval in the circumferential direction; and a second oil-repellent film covers the surface of the aforementioned retainer and has oil-repellent properties for the aforementioned lubricant.

3. The harmonic gear device as described in claim 2, wherein, The first and second oil-removing films mentioned above are fluoropolymer films.

Images