Strain wave gear device

Abstract

A strain wave gearing device (1) is provided with a hollow input shaft (5), and a wave generator (4) that bends an external gear (3) in the radial direction and meshes with an internal gear (2) is provided with a wave bearing (43) having a ball holder (47). An input shaft outer peripheral surface portion of the hollow input shaft (5) located inside the externally toothed gear (3) is covered by an oleophobic coating (14). The surface of the ball holder (47) is also covered by the oleophobic film (15). As a result, the grease stirring resistance of the hollow input shaft (5) and the ball holder (47) can be reduced by the oleophobic films (14, 15), and the loss torque of the strain wave gear device (1) can be reduced.

Description

Technical Field

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

[0002] It is known that a wave gear device is widely used as a speed reducer and has an input shaft that transmits high-speed rotation from a motor or the like to a wave generator. One of the requirements for a wave gear device is to reduce loss torque. When a wave gear device is operated, loss torque is generated due to friction resistance of the meshing portion of the gear, rolling resistance of the bearing, stirring resistance of grease (lubricant), etc., and part of the energy of the input shaft rotation is converted into heat. By reducing the above-mentioned loss torque, the following advantages are realized: low heat generation and low capacity of the drive motor can be achieved.

[0003] Since the stirring resistance of the grease increases as the stirring speed increases, the stirring resistance near the input shaft of the wave gear device used at a high speed of several thousand revolutions per minute accounts for a large proportion of all the torque loss. In addition, a large amount of grease is applied near the input shaft and the wave bearing in order to maintain long-term lubricity, so the grease contacts not only the vicinity of the ball of the wave bearing but also the input shaft, which is one of the reasons for the increase in stirring resistance.

[0004] As a method of reducing stirring resistance, it is possible to reduce the viscosity of the grease base oil and reduce the amount of coating. However, both of them have a trade-off relationship with lubricity, and it is difficult to further improve the existing products when the loss torque and lubricity are designed in consideration of the balance between them.

[0005] In addition, regarding a wave gear device, a proposal has been made to form an oil-repellent portion having a higher oil-repellency than the surface of the teeth of the external gear on the surface of the body of the external gear in order to reduce the lubricant flowing out from the meshing portion between the internal gear and the external gear (Patent Document 1).

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2018-53912 Summary of the invention

[0009] In the case of a wave gear device, grease located near the input shaft and near the balls of the wave bearing contacts or adheres to the input shaft, the retainer of the wave bearing, etc. This contact of grease increases the stirring resistance, thereby increasing the loss torque of the wave gear device.

[0010] An object of the present invention is to provide a wave gear device capable of suppressing an increase in loss torque due to an increase in stirring resistance near an input shaft and a wave bearing caused by a lubricant.

[0011] The wave gear device of the present invention comprises:

[0012] Rigid internal gears;

[0013] a flexible external gear coaxially disposed inside the internal gear;

[0014] a wave generator including a wave plug and a wave bearing mounted between a non-circular outer peripheral surface of the wave plug and an inner peripheral surface of the external gear;

[0015] an input shaft coaxially mounted to the wave plug;

[0016] an input shaft outer peripheral surface portion located inside the externally toothed gear of the input shaft; and

[0017] A first oil-repellent coating such as a fluororesin coating partially covers the outer peripheral surface of the input shaft and has oil repellency with respect to a lubricant applied or supplied to the wave bearing.

[0018] In addition, regarding the wave gear device of the present invention,

[0019] The wave bearing has:

[0020] Inner and outer rings;

[0021] a plurality of rolling elements which are inserted in a rollable state into an annular raceway groove formed between the inner ring and the outer ring;

[0022] a retainer that retains the rolling element at positions spaced apart in the circumferential direction; and

[0023] A second oil-repellent coating such as a fluororesin coating covers the surface of the retainer and has oil-repellent properties with respect to the lubricant.

[0024] Effects of the Invention

[0025] The wave gear device of the present invention can obtain the following effects, thereby making it possible to reduce the loss torque of the wave gear device.

[0026] (1) Reduction in the amount of lubricant adhered: The lubricant is easily thrown out by centrifugal force through the oleophobic coating, so that the amount of lubricant adhered is reduced, thereby reducing the stirring resistance.

[0027] (2) Reduction of lubricant shear rate: The oleophobic coating causes sliding between the surface in contact with the lubricant and the lubricant, thereby reducing the lubricant shear rate and thereby reducing stirring resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic longitudinal sectional view of a wave gear device according to an embodiment of the present invention.

[0029] Figure 2 It is shown Figure 1 Illustration of the grease lubricated portion of a wave gear device. DETAILED DESCRIPTION

[0030] Below, refer to Figure 1 and Figure 2 A wave gear device according to an embodiment of the present invention will be described. The wave gear device 1 includes: a rigid internal gear 2; a flexible external gear 3 formed in a top hat shape; a wave generator 4; a hollow input shaft 5; and a main bearing 6 composed of a cross roller bearing, which supports the external gear 3 in a state of free rotation relative to the internal gear 2. In addition, the wave gear device 1 includes: a fixed side end plate 7 formed integrally with the internal gear 2; and an output side end plate 8, which is an output shaft coaxially fastened and fixed to the external gear 3. One shaft end 51 of the hollow input shaft 5 is supported by the fixed side end plate 7 in a state of free rotation via a bearing 9a, and the other shaft end 52 of the hollow input shaft 5 is supported by the output side end plate 8 in a state of free rotation via a bearing 9b.

[0031] The internal gear 2 is formed in an annular shape and has internal teeth 21 formed on its circular inner circumferential surface. A fixed-side end plate 7 is integrally formed on the end surface portion of the internal gear 2 on the side of the shaft end 51 in the axial direction. An inner ring 61 of the main bearing 6 is coaxially fastened and fixed to the other side of the internal gear 2 in the axial direction.

[0032] The external gear 3 includes: a cylindrical body 32 formed with external teeth 31; a diaphragm 33 extending radially outward from the end of the cylindrical body 32; and an annular boss 34 formed integrally with the outer peripheral edge of the diaphragm 33. The cylindrical body 32 is coaxially arranged inside the internal gear 2 and the inner ring 61 of the main bearing 6, and the external teeth 31 are opposite to the internal teeth 21 and can mesh with the internal teeth 21. The boss 34 is located between the outer ring 62 of the main bearing 6 and the output side end plate 8 in the axial direction. The three components of the outer ring 62, the boss 34 and the output side end plate 8 are coaxially fastened and fixed.

[0033] The wave generator 4 includes: a wave plug 42 having an elliptical outer peripheral surface 41 of a certain width formed integrally on the outer peripheral surface of the hollow input shaft 5; and a wave bearing 43. The wave bearing 43 is mounted between the elliptical outer peripheral surface 41 of the wave plug 42 and the inner peripheral surface 35 of the cylindrical body portion 32 of the external gear 3 on which the external teeth 31 are formed. The wave bearing 43 includes: a flexible inner ring 44; a flexible outer ring 45; a plurality of balls 46 inserted between the inner ring 44 and the outer ring 45 in a rollable state; and an annular ball retainer 47 that retains the balls 46 at a certain interval in the circumferential direction.

[0034] Inside the wave gear device 1, and on the outside of the external gear 3, an outer peripheral gap portion 11 surrounded by the inner ring 61 of the main bearing 6, the external gear 3, and the internal gear 2 is formed. The outer peripheral gap portion 11 extends along the outer peripheral surface of the cylindrical body portion 32 of the external gear 3, and is connected to the meshing portion of the internal teeth 21 and the external teeth 31. In addition, an inner peripheral gap portion 12 surrounded by the external gear 3, the hollow input shaft 5, the fixed side end plate 7, and the output side end plate 8 is formed inside the external gear 3. The wave bearing 43 is located in the inner peripheral gap portion 12.

[0035] Lubricant is applied or supplied to the lubricated parts inside the wave gear device 1. The main lubricated parts are the meshing parts between the internal teeth 21 and the external teeth 31, the wave bearing 43 of the wave generator 4, and the sliding parts between the outer ring 45 of the wave bearing 43 and the inner peripheral surface of the external gear 3. For example, Figure 2 As shown in the middle grid-shaded portion G, grease is applied or filled in the inner peripheral gap portion 12 and inside and around the wave bearing 43 .

[0036] As described above, the higher the stirring speed, the greater the stirring resistance of the grease. Therefore, the stirring resistance near the hollow input shaft 5 used at a high speed of several thousand revolutions per minute accounts for a large proportion of the total loss torque of the wave gear device 1. In addition, a large amount of grease is applied near the hollow input shaft 5 and the wave bearing 43 in order to maintain long-term lubricity. Therefore, the grease contacts not only the vicinity of the ball 46 of the wave bearing 43 but also the hollow input shaft 5, which is one reason for the increase in stirring resistance.

[0037] In order to avoid such disadvantages, the wave gear device 1 is coated with an oil-repellent coating such as a fluorine coating having oil-repellent properties to grease to cover the outer peripheral surface of the hollow input shaft 5 located inside the external gear 3. Figure 2As shown, the input shaft outer peripheral surface portions 53 and 56 on both sides of the wave plug 42 and the end surface portions 54 and 55 on both sides of the wave plug 42 are covered with the oil-repellent coating 14. In addition, in this example, the entire surface of the ball retainer 47 of the wave bearing 43 is also covered with the oil-repellent coating 15 such as a fluorine coating. The oil-repellent coating 14 and the oil-repellent coating 15 may be the same type of oil-repellent coating. The oil-repellent coatings 14 and 15 may be different types of oil-repellent coatings. In addition, the oil-repellent coatings 14 and 15 may be the same coating thickness or different coating thicknesses. The oil-repellent coatings 14 and 15 are formed of 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.

[0038] Regarding the wave gear device 1, the wave generator 4 with an elliptical profile is embedded in the portion of the external gear 3 formed with the external teeth 31 on the inner side, and is bent into an elliptical shape, and the portion of the external teeth 31 located at the long axis position of the elliptical shape and in the vicinity thereof meshes with the internal teeth 21. The hollow input shaft 5 is connected to the output shaft of a motor (not shown) and the hollow input shaft 5 is driven to rotate at a high speed. When the wave plug 42 of the wave generator 4 is formed integrally with the hollow input shaft 5 and rotated at a high speed, the meshing position of the external gear 3 relative to the internal gear 2 moves in the circumferential direction. The number of teeth of the internal gear 2 is 2n (n: a positive integer) more than the number of teeth of the external gear 3. A relative rotation corresponding to the difference in the number of teeth is generated between the two gears 2 and 3. The internal gear 2 is on the fixed side, and the decelerated rotation after the input rotation is greatly decelerated is taken out from the external gear 3 to the load side (not shown) via the output side end plate 8.

[0039] Here, the input shaft outer peripheral surface portions 53 and 56 of the hollow input shaft 5 rotating at high speed and the end surface portions 54 and 55 on both sides of the wave plug 42 are covered with the oleophobic coating 14. In addition, the surface of the ball retainer 47 rotating at a predetermined speed together with the ball 46 as the hollow input shaft 5 rotates at high speed is also covered with the oleophobic coating 15. If the hollow input shaft 5 rotates at high speed, the grease is easily thrown out by the oleophobic coating 14 by centrifugal force, so that the amount of grease attached to the hollow input shaft 5 is reduced, and the grease stirring resistance is reduced. Similarly, with respect to the ball retainer 47 rotating at a predetermined speed, the grease is easily thrown out by the oleophobic coating 15 by centrifugal force, so that the amount of grease attached to the ball retainer 47 is reduced. Since the amount of grease attached is reduced, the grease stirring resistance acting on the hollow input shaft 5 and the ball retainer 47 is reduced.

[0040] In addition, due to the oleophobic coating 14, sliding occurs between the input shaft outer peripheral surface 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, which are in contact with the grease, and the grease shear rate is reduced, thereby reducing the grease stirring resistance acting on the hollow input shaft 5. Similarly, due to the oleophobic coating 15, sliding occurs between the surface of the ball retainer 47 in contact with the grease and the grease, thereby reducing the grease shear rate and reducing the grease stirring resistance acting on the ball retainer 47.

[0041] In this way, the grease stirring resistance acting on the hollow input shaft 5 and the ball retainer 47 can be reduced by the oil-repellent coatings 14 and 15 , so that the loss torque of the wave gear device 1 can be reduced.

[0042] (Other embodiments)

[0043] The above-mentioned embodiment applies the present invention to a top-hat type wave gear device having a top-hat-shaped external gear. The present invention can also be applied to other types of wave gear devices. For example, it can also be applied to a cup-type wave gear device having a cup-shaped external gear, and it can also be applied to a flat type wave gear device having a driving side internal gear, a stationary side internal gear, and a cylindrical external gear.

Claims

1. A wave gear device, comprising: Rigid internal gears; a flexible external gear coaxially disposed inside the internal gear; a wave generator including a wave plug and a wave bearing mounted between a non-circular outer peripheral surface of the wave plug and an inner peripheral surface of the external gear; an input shaft coaxially mounted to the wave plug; an input shaft outer peripheral surface portion, which is located inside the external gear of the input shaft; as well as The first oil-repellent coating partially covers the outer peripheral surface of the input shaft and has oil-repellent property with respect to the lubricant applied to or supplied to the wave bearing.

2. The wave gear device according to claim 1, characterized in that: The wave bearing has: Inner and outer rings; a plurality of rolling elements which are inserted in a rolling manner into an annular raceway groove formed between the inner ring and the outer ring; a retainer that retains the rolling element at positions spaced apart in the circumferential direction; and The second oleophobic coating covers the surface of the retainer and has oleophobicity to the lubricant.

3. The wave gear device according to claim 2, characterized in that: The first oleophobic film and the second oleophobic film are fluororesin films.

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