Strain Wave Gear

Abstract

The invention relates in particular to a strain wave gear for industrial robots, comprising a first assembly (2) on which a flexible gear element formed as a flanged bush (8) is fixed, provided with an external toothing (11), a wave generator (16) intended to deform the flexible gear element (8), and an output assembly (12) having an internal toothing (14) meshing with the external toothing (11) of the flexible gear element (11). The output assembly (12) is mounted in the first assembly (2) by means of rolling bearings (34) which are in each case sealed towards both sides by seals (30, 40) which are effective between the first assembly (2) and the output assembly (12), one of these two seals (40) defining, on the side of said seal facing away from the rolling bearings (34), a lubricant chamber which extends to the teeth (11, 14) of the flexible gear element (8) and to the output assembly (12).

Description

[Technical Field]

[0001] The present invention relates to a strain wave gear according to the preamble of claim 1, suitable for use as an actuating gear mechanism in, for example, an industrial robot. [Background technology]

[0002] A typical actuating gear mechanism is known, for example, from DE 10 2016 207 612 A1. The known strain wave gear has a component with flexible teeth in the form of a flanged bush, which is at least indirectly attached to a surrounding component. A component with rigid teeth is rotatably arranged within the surrounding component, which acts as an output element of the strain wave gear and directly cooperates with the component with flexible teeth. Static seals are located at various points in the known strain wave gear.

[0003] Various embodiments of strain wave gears in which a flanged bush is mounted in an assembly that is rotatable as a whole are known, for example from the literature, DE 102018128930 A1, WO 2017 / 206988 A1 and DE 102017128423 A1. The three cases mentioned relate to strain wave gears in electromechanical camshaft adjusters.

[0004] German Patent Application No. 102017119461 discloses a rolling bearing for a strain wave gear. The inner ring of the rolling bearing has an elliptical circumferential contour. A seal is arranged between the inner and outer rings of the rolling bearing, and the seal is supported by the inner ring so as to be rotatably fixed and abuts against the outer ring with the elliptical circumferential contour.

[0005] German Patent No. 102017114175 discloses a strain wave gear with a flexible gear element, which features a modified collar shape. In this case, the inner and outer edges of the flat, annular, disc-shaped portion of the flexible gear element are fitted within a cylindrical portion, with external toothing located on the inner cylindrical portion, and the outer cylindrical portion is significantly shorter than the inner cylindrical portion in the axial direction of the gear element, and thus the entire strain wave gear. Even with this modified collar shape, the flexible gear element is still encompassed by the term flanged bushing. Generally, flanged bushings have a sleeve-shaped portion with external toothing, to which a radially outwardly facing annular disc-shaped portion, i.e., a collar, is connected. Typically, the external toothing of the sleeve-shaped portion is located only in the area of ​​the sleeve-shaped portion spaced from the collar.

[0006] A manipulator arm for a robot is already known from DE 10 2020 107 990 A1. The manipulator arm is adjustable by means of a printed circuit board motor and a gearbox, whereby the gearbox can be configured as a strain wave gear, a cycloid gear or a planetary gear. Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to specify a strain wave gear that is particularly suitable for use in industrial robots and that represents a further advancement over the prior art, particularly with regard to the aspect of lubrication technology. [Means for solving the problem]

[0008] According to the present invention, this object is achieved by a strain wave gear having the features of claim 1. The strain wave gear comprises a first assembly configured as a flanged bush and fitted with a flexible gear element provided with external toothing, and a wave generator provided for deforming the flexible gear element. The output assembly of the strain wave gear has internal toothing that meshes with the external toothing of the flexible gear element. The output assembly is mounted in the first assembly by means of a rolling bearing, which is sealed on both sides by seals acting between the first assembly and the output assembly. One of these two seals, the inner seal, defines a lubricant chamber on the side of the seal facing away from the rolling bearing, which extends to the toothing of the flexible gear element and the output assembly.

[0009] The present invention is based on the observation that actuation gear mechanisms often used in robots do not have rotation angle limits, which can initiate grease migration that leads to a pressure increase in the actuation gear mechanism, along with a pumping effect caused by permanent deformation of the flexible gear element, specifically the rolling of the teeth of the flexible gear element on the rigid gear element. Conventional solutions, along with the lack of ventilation and the temperature increase that occurs during operation, which can be caused by friction and servo motors, ultimately lead to the risk of grease leakage from the actuation gear mechanism.

[0010] This risk is effectively counteracted in the strain wave gear according to the present application by having one of the seals, called the inner seal to distinguish it from the other seals, separate the first lubrication space, i.e. the space in which the rolling bearing supporting the output assembly is located, from the second space, i.e. the space in which the mating teeth of the flanged bush are located on the one hand and the output assembly is located on the other hand, the latter space also commonly called the lubricant space.

[0011] A particular advantage is the fact that the lubricant chamber, on the one hand, and the rolling bearing supporting the output assembly, on the other, can be filled with different lubricants. Specifically, the contact surface between the flanged bushing's teeth and the internal output toothing can be lubricated with a relatively thin, i.e., low-viscosity grease, while the rolling bearing is lubricated with a relatively high-viscosity grease. The good fluidity of the grease in the lubricant chamber, i.e., in the chamber extending to the flanged bushing's teeth and the output assembly, is adapted to the high speed of the wave generator. Compared to the speed of the wave generator, the output element can only be pivoted slowly due to the characteristics of the strain wave gear as a highly reduced-speed operating gear mechanism.

[0012] On the other hand, the bearings by which the output assembly is mounted within the first assembly must absorb relatively large forces. Both aspects, both the relative velocities that occur and the forces acting within the strain wave gear, highlight the advantage of using a relatively viscous or high viscosity lubricant to lubricate the rolling bearings, generally referred to as main bearings by which the output assembly is mounted within the first assembly.

[0013] Both the lubricant immediately surrounding the flanged bushing, i.e., located in the aforementioned lubricant chamber, and the lubricant lubricating the main bearing can be grease. Alternatively, for example, the lubricant chamber can be lubricated with oil and the main bearing with grease. In all cases, the internal seal ensures that the different lubricants do not mix, or only slightly mix.

[0014] The inner seal is located, for example, between the front of the output assembly and the collar of the flexible gear element. Compared to the external teeth of the flanged bushing, the collar of the flanged bushing deforms relatively little, even if significant deformation of the collar occurs, during operation of the strain wave gear. This allows the inner seal, located at the front of the output assembly, to absorb only small relative axial movements of the rotating elements of the strain wave gear. Because the collar of the flexible gear element is rigidly connected to the first assembly while the output assembly rotates, the inner seal is a dynamic seal. Specifically, the inner seal can be configured as a contact seal that contacts the collar of the flexible gear element. For example, the seal has a metal core inserted into a front groove in the output assembly.

[0015] The conforming sealing element, typically made of an elastomeric material surrounding an optional metal core, can have a single sealing lip or an arrangement of several sealing lips that abut against the collar of the flexible gear element, thereby providing a one-sided or two-sided sealing effect. In modified embodiments, a felt ring or PTFE ring, such as those used in packing pumps, can also be used as an internal seal for strain wave gears.

[0016] According to a possible further development, the strain wave gear includes a third seal fastened to the first housing assembly. Specifically, the third seal can be held on a cylindrical inner portion of the first housing assembly. In a particularly compact configuration, a plane perpendicular to the rotation axis of the strain wave gear, i.e., a radial plane, exists that intersects both the third seal and the inner seal. In addition, this plane can also intersect with the rolling bearing by which the output assembly is mounted in the first assembly.

[0017] Alternatively, a third seal mounted to the first housing assembly can contact the collar of the flexible gear element opposite the seal that defines the lubricant chamber extending to the teeth of the flanged bushing and the output assembly.

[0018] The rolling bearing by which the output assembly is supported within the first assembly is also called the main bearing. The main bearing is, for example, a double-row bearing, specifically a two-row angular contact roller bearing. The raceway of the rolling bearing can be formed by the same component of the output assembly in which a seal is inserted, and the seal defines a lubricant space that extends to the teeth of the flexible gear element and the output assembly.

[0019] The strain wave gear's output assembly, either as a whole or in part, can have a cylindrical basic shape, positioned radially outside the external toothing of the flexible gear element and radially inside a portion of the first assembly. At the same time, the output assembly or a portion of this assembly can be positioned radially outside a portion of the first assembly. This latter portion is specifically where the third seal is located. In contrast to the inner seal, the third seal only needs to accommodate small relative movements, and is therefore also referred to as a quasi-static seal. This seal does not require a metal core. This allows the strain wave gear to have a variety of seals that can be configured differently depending on the individual requirements.

[0020] In the following, exemplary embodiments of the invention will be explained in more detail with reference to the drawings. [Brief explanation of the drawings]

[0021] [Figure 1] A cross-sectional view of a strain wave gear is shown. DETAILED DESCRIPTION OF THE INVENTION

[0022] The strain wave gear designated by reference number 1 is intended as an actuation gear mechanism for an industrial robot, not shown in detail. With regard to the main function of the strain wave gear 1, reference is made to the prior art cited at the outset.

[0023] The strain wave gear 1 is rigidly connected to the robot arm and comprises a first assembly 2, also referred to without limiting generality as a housing assembly. The housing assembly 2 comprises several housing components 3, 4, 5. The first housing component 3 is ring-shaped, as is the second housing component 4, while the third housing component 5 extends further in the direction of the central axis of the strain wave gear 1 and has an inner part 7 with a cylindrical basic shape.

[0024] 1, the three housing components 3, 4, 5 form a U-shape, with an annular circumferential space between the inner part 7 and the housing components 3, 4, into which the output assembly 12 of the strain wave gear 1 is engaged. The output assembly 12 is connected to another robot arm or to the end effector of the robot to be adjusted. The static seal in the housing assembly 2 is designated 6, and the static seal in the output assembly 12 is designated 45.

[0025] The housing components 3, 4, 5 are rigidly connected to one another by screw connections (not shown). Furthermore, a flexible gear component 8 configured as a flanged bushing is connected to the housing components 3, 4, 5. A collar of the flexible gear component 8, designated 9, is fixed between the intermediate housing component 4 and the housing component 5. In its region projecting radially inward beyond the housing disc 6, the collar 9 is at least slightly elastically flexible. Adjacent to the inner edge of the collar 9 is a sleeve-like portion 10 of the flexible gear component 8, which is also elastically displaceable. The sleeve-like portion 10 has external toothing 11 that is spaced apart from the collar 9 and extends to the end face of the flanged bushing 8 opposite the collar 9. The external toothing 11 partially meshes with the internal toothing 14 of a ring gear 13, which is assigned to an output-side assembly 12. The output assembly 12 further comprises an annular output element 15 which is rigidly connected to the ring gear 13, rotatably mounted on the first assembly 2 and located in the annular circumferential region.

[0026] To deform the flexible gear component 8 during operation of the strain wave gear 1, a wave generator 16 is provided. In this case, the wave generator 16 has a shaft 17, which at the same time forms the inner ring of the rolling bearing on which the rolling elements 18, i.e., balls, guided within a cage 19, roll. The inner ring of the rolling bearing 17 is essentially rigid and has an elliptical rather than circular shape. The corresponding outer ring 20 is elastically flexible and adapts to the non-circular shape of the inner ring of the rolling bearing 17. As a result, the outer toothing 11 is engaged with the inner toothing 14 at two diametrically opposed points, while the inner toothing 14 is otherwise lifted from the outer toothing 11. The area of ​​the sleeve-like part 10 provided with the outer toothing 11 rests loosely on the outer ring 20. The slightly different number of teeth of the external toothing 11 on the one hand and the internal toothing 14 on the other hand ensures, in a manner known per se, that a complete rotation of the shaft 17 is converted into only a slight pivoting movement between the first assembly 2 and the output assembly 12.

[0027] In the illustrated embodiment, the shaft 17 is mounted to the housing assembly 2 by a ball bearing 21. The ball bearing 21 has an inner ring 22, a seal 23, and an outer ring 24 inserted into the housing component 5. The outer ring 24 is inserted into the cylindrical inner surface of the inner portion 7.

[0028] The seal 25 is carried on the housing component 5 of the first assembly 2 in a flat annular disc-shaped area radially outward of the inner part 7, said seal being in contact with the collar 9 on its outer side, i.e. on the side of said seal facing away from the sleeve-like part 10. The seal 25 acts as a quasi-static seal.

[0029] The outer circumferential surface of the sleeve-like portion 10 defines a cavity, which is further defined by the output assembly 12, thereby forming a substantially concentric arrangement between the sleeve-like portion 10 and the annular output element 15. On the side of the sleeve-like portion 10 facing away from the collar 9, the cavity extends to the toothings 11, 14. The toothings 11, 14 are lubricated with a lubricant, i.e., grease, which is free to move within the cavity, as illustrated by the arrows in FIG. 1 . In this case, the lubricant flow can be induced, in particular, by deformation of the gear component 8. The cavity serves as a lubricant space extending axially over the entire length of the sleeve-like portion 10. In the radial direction, the lubricant chamber has a non-uniform thickness. Among other things, the lubricant chamber is defined by an annular circumferential web 26, which is formed on the inner periphery of the ring gear 13, adjacent to the internal toothings 14, and axially overlapping the annular output element 15. On the front side of the ring gear 13 facing away from the annular web 26, there is a mounting part 27 configured as a cap, which serves as a barrier for the lubricant that lubricates the teeth 11, 14 and also the wave generator 16. A cylindrical part 28 of the mounting part 27 is held on the outer circumferential surface of the ring gear 13.

[0030] The annular output element 15 is connected to the ring gear 13 at the front and has an outer sealing portion 29. A seal 30 acts between the sealing portion 29, which serves as a cylindrical outer surface, and the first housing component 3. The seal 30 is configured as a contact seal with a metal core 31 and a surrounding sealing element 32 made of elastomer. The sealing lip of the seal 30 is indicated by 33. Axial-side to the seal 30 is a main bearing 34, which mounts the output assembly 12 in the housing assembly 2. In this case, the main bearing 34 is configured as a double-row angular contact roller bearing with rows of rolling elements designated 35 and 36. The rolling elements, i.e., rollers, designated 37, are arranged in an X-array in the main bearing 34, i.e., the rolling bearing, and are guided in a cage 38. The double-row rolling bearing 34 is capable of absorbing radial, axial, and tilting loads. The main bearing 34 is sealed at one of its end faces by a seal 30 and is lubricated with a grease that is more viscous than the lubricant used to lubricate the flexible gear component 8 .

[0031] On the opposite side, the main bearing 34 is sealed by a seal 40 located in the front seal section 39, also referred to as the inner seal. The seal 40 is located opposite the seal 25. The metal core of the seal 40 is designated 41, the seal element 42, and the seal lip 43. Overall, the seal 40, whose basic structure corresponds to that of the seal 30, aside from the different orientation of the elements 41 and 42, is inserted into a front groove 44 of the annular output element 15. The seal lip 43 rests on the collar 9. With regard to lubrication, the seal 40 separates the space in which the main bearing 34 is located from the space in which the lubricated teeth 11 and 14 are located. Therefore, there is no significant mixing of different lubricants. Depending on the application, the lubrication can be configured as a lifetime lubrication or provide the option for relubrication. [Explanation of symbols]

[0032] 1 Strain Wave Gear 2 Housing Assembly, First Assembly 3 First Housing Component 4 Secondary Housing Component 5 Third Housing Component 6 Seal in the first assembly 7 inner portion of first housing component 8 Flexible Gear Components 9 Flexible Gear Component Colors 10 Sleeve-like portion of flexible gear component 11 External teeth 12 Output side assembly 13 Ring Gear 14 Internal teeth 15 Circular output element 16 Wave Generator 17 Inner ring, adjustment shaft 18 Rolling elements 19 Cage 20 outer ring 21 Ball bearings 22 Inner ring of ball bearing 23 Ball bearing seal 24 outer ring of ball bearing 25 seal between inner part 7 and gear component 8 26 Circular Web 27 Mounting part 28 Cylindrical part of mounting part 29 Outer seal portion of output element 15 30 stickers 31 Metal Core 32 sealing elements 33 Seal lip 34 Double-row rolling bearings, main bearings 35 Rolling element array 36 Rolling element array 37 Rolling element row, roller 38 Cage 39 Front seal part 40 seal between element 15 and gear component 8, inner seal 41 Metal Core 42 sealing elements 43 Seal lip 44 Front gutter 45 Seal in output assembly

Claims

1. A strain wave gear having a first assembly (2) configured as a flanged bush (8) and having a flexible gear element provided with external toothing (11) attached thereto, a wave generator (16) provided for deforming the flexible gear element (8), and an output side assembly (12) having internal toothing (14) that meshes with the external toothing (11) of the flexible gear element (11), wherein the output side assembly (12) is supported by a rolling bearing (34). the rolling bearing (34) is mounted in a first assembly (2), and is sealed on both sides by seals (30, 40) acting between the first assembly (2) and the output-side assembly (12), the inner seal (40) of these two seals defining a lubricant chamber on the side of the seal facing away from the rolling bearing (34), the lubricant chamber extending to the teeth (11, 14) of the flexible gear element (8) and the output-side assembly (12); a seal lip (43) of the inner seal (40) that defines a lubricant space and is disposed between an end face of the output side assembly (12) and a collar (9) of the flexible gear element (8), the seal lip (43) of the inner seal (40) being placed in contact with the collar (9).

2. 2. The strain wave gear according to claim 1, wherein the inner seal (40) has a metal core (41) inserted into a front groove (44) of the output assembly (12).

3. 3. The strain wave gear according to claim 1, characterized by a third seal (25) that contacts the collar (9) of the flexible gear element (8) and is opposite the inner seal (40) that defines the lubricant space extending to the teeth (11, 14) of the flexible gear element (8) and the output side assembly (12).

4. 4. A strain wave gear according to claim 3, characterized in that the third seal (25) is carried on the first housing assembly (2).

5. 2. The strain wave gear according to claim 1, wherein the output side assembly (12) has a cylindrical basic shape located radially outside the external toothing (11) of the flexible gear element (8) and radially inside a portion of the first assembly (2).

6. 2. The strain wave gear according to claim 1, wherein the rolling bearing (34), by which the output assembly (12) is mounted within the first assembly (2), is configured as a double-row angular contact roller bearing.

7. 7. A strain wave gear according to claim 6, characterized in that the raceway of the rolling bearing (34) is formed by the same component (15) of the output side assembly (12) into which the seal (40) is inserted, the inner seal (40) defining the lubricant space extending to the teeth (11, 14) of the flexible gear element (8) and the output side assembly (12).

8. 2. A strain wave gear according to claim 1, characterized in that on the one hand the rolling bearing (34) and on the other hand the lubricant chamber separated from the rolling bearing (34) by the inner seal (40) and extending to the teeth (11, 14) are filled with different lubricants.

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