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 which is suitable for use as an actuating gear mechanism, e.g. in an industrial robot. [Background technology]

[0002] A typical actuating gear mechanism is known, for example, from DE 102016207612 A1. The known strain wave gear has a component with flexible toothing in the form of a flanged bush, which is at least indirectly attached to a surrounding component. A component with rigid toothing 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 toothing. 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 which is rotatable as a whole are known, for example in 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 adjustment devices.

[0004] DE 10 2017 119 461 A1 discloses a rolling bearing for strain wave gears, the inner ring of which has an elliptical circumferential contour. Between the inner and outer rings of the rolling bearing, a seal is arranged, which is supported on the inner ring in a rotatably fixed manner and rests against the outer ring with an elliptical circumferential contour.

[0005] DE 102017114175 discloses a strain wave gear with a flexible gear element, which depicts a modified collar shape. In this case, the inner and outer edges of the flat annular disk-shaped part of the flexible gear element are fitted together in a cylindrical part, on which the external toothing is located and which is made significantly shorter than the inner cylindrical part in the axial direction of the gear element and thus of the entire strain wave gear. Even with this modified collar shape, the flexible gear element is encompassed by the term flanged bushing. Generally, flanged bushings have a sleeve-shaped part with external toothing, to which a radially outwardly facing annular disk-shaped part, i.e. a collar, is connected. Typically, the external toothing of the sleeve-shaped part is located only in the area of ​​the sleeve-shaped part that is remote from the collar.

[0006] A manipulator arm for a robot is already known from DE 10 2020107 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 which is particularly suitable for use in industrial robots and which 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 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, on which a flexible gear element provided with an external toothing is mounted, and a wave generator provided for deforming the flexible gear element. The output assembly of the strain wave gear has an internal toothing meshing 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 said seal facing away from the rolling bearing, which lubricant chamber extends up to the toothing of the flexible gear element and to the output assembly.

[0009] The invention is based on the consideration that actuation gear mechanisms often used in robots do not have rotation angle limits, which allows the initiation of grease migration leading to a pressure increase in the actuation gear mechanism, together with a pumping effect caused by the permanent deformation of the flexible gear element, in particular the rolling of the teeth of the flexible gear element on the rigid gear element. Conventional solutions, together with the lack of ventilation and the temperature increase that occurs during operation, which may 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 a first lubrication space, i.e. the space in which the rolling bearing supporting the output assembly is located, from a second space, i.e. the space in which, on the one hand, the meshing teeth of the flanged bush are located and, on the other hand, the output assembly, 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 hand can be filled with different lubricants. In particular, the contact surface between the toothing of the flanged bush and the internal toothing of the output 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 toothing of the flanged bush and in the chamber extending to the output assembly, is adapted to the high speed of the wave generator. Compared to the speed of the wave generator, the output element is only pivoted slowly due to the properties of the strain wave gear as a highly reduced 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 arise 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 the 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 above-mentioned 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 toothing of the flanged bush, the collar of the flanged bush deforms relatively little, if at all, during operation of the strain wave gear. This allows the inner seal located at the front of the output assembly to absorb only a small relative axial movement of the rotating elements of the strain wave gear. The inner seal is a dynamic seal, since the collar of the flexible gear element is rigidly connected to the first assembly, while the output assembly rotates. In particular, 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 that is inserted into a front groove of the output assembly.

[0015] The compliant 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, thus providing a one-sided or two-sided sealing effect. In a modified embodiment, a felt or PTFE ring, such as those used in packing pump packings, can also be used as an internal seal for strain wave gears.

[0016] According to a possible further development, the strain wave gear comprises a third seal fastened to the first housing assembly. In particular, the third seal can be held on a cylindrical inner part of the first housing assembly. In a particularly compact configuration, there is a plane perpendicular to the rotation axis of the strain wave gear, i.e. a radial plane, which 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 that extends to the teeth of the flanged bushing and the output assembly.

[0018] The rolling bearing by which the output assembly is supported in the first assembly is also called the main bearing. The main bearing is, for example, a double row bearing, in particular 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, the seal defining a lubricant space extending to the teeth of the flexible gear element and the output assembly.

[0019] The output assembly of the strain wave gear, as a whole or with a part of this assembly, can be described as a cylindrical basic shape located radially outside the external toothing of the flexible gear element and at the same time radially inside a part of the first assembly. At the same time, the output assembly or a part of this assembly can be located radially outside a part of the first assembly. The latter part is specifically the part where the third seal is located. In contrast to the inner seal, the third seal only has to absorb small relative movements and is therefore also called a quasi-static seal. In this seal, no metal core is required. This allows the strain wave gear to have various seals that can be configured differently depending on the respective requirements.

[0020] Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. [Brief description of the drawings]

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

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

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

[0024] Overall, the three housing components 3, 4, 5 thus describe a U-shape in the cross section shown in Figure 1, with an annular circumferential space existing between the inner part 7 and the housing components 3, 4, in 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 an end effector of a 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 means of a screw connection (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 area where it projects radially inwards 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 part 10 of the flexible gear component 8, which is also elastically displaceable. The sleeve-like part 10 has an 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 an 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] In order to deform the flexible gear component 8 during operation of the strain wave gear 1, a wave generator 16 is provided. In the present case, the wave generator 16 has a shaft 17 which at the same time forms a rolling-bearing inner ring on which rolling elements 18, i.e. balls, which are guided in a cage 19, roll. The rolling-bearing inner ring 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 rolling-bearing inner ring 17. As a result, the external toothing 11 is engaged with the internal toothing 14 at two diametrically opposed points, while the internal toothing 14 is otherwise lifted off the external toothing 11. The area of ​​the sleeve-like part 10 provided with the external toothing 11 is loosely resting 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 translated into only a slight pivoting movement between the first assembly 2 and the output assembly 12.

[0027] In the embodiment shown, the shaft 17 is mounted in 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 that are 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 and is 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, and is thus arranged substantially concentrically 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 can move freely in the cavity, as illustrated by the arrows in FIG. 1. In this case, the flow of the lubricant can be caused in particular by deformations of the gear component 8. The cavity serves as a lubricant space extending over the entire length of the sleeve-like portion 10 detected in the axial direction. In the radial direction, the lubricant chamber has a non-uniform thickness. In particular, the lubricant chamber is defined by an annular circumferential web 26, which is formed on its inner circumference by the ring gear 13, adjoins the internal toothing 14 and overlaps the annular output element 15 in the axial direction. At 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 at the front to the ring gear 13 and has an outer sealing part 29. Between the sealing part 29, which serves as a cylindrical outer periphery, and the first housing component 3, a seal 30 acts. 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 with 33. Axial next to the seal 30 is the main bearing 34, by means of which the output assembly 12 is mounted 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, 36. The rolling elements, i.e. rollers, designated 37, are arranged in an X-arrangement 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 tilt 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 part 39, called the inner seal. The seal 40 is opposite the seal 25. In the case of the seal 40, the metal core is designated 41, the sealing element 42 and the sealing lip 43. Overall, the seal 40, whose basic structure corresponds to that of the seal 30, apart from the different orientation of the elements 41, 42, is inserted in a front groove 44 of the annular output element 15. The sealing lip 43 rests on the collar 9. The seal 40 separates, in terms of lubrication, the space in which the main bearing 34 is located from the space in which the lubricated toothings 11, 14 are located. There is therefore no significant mixing of the different lubricants. Depending on the application, the lubrication can be configured as a lifelong lubrication or the option for relubrication can be provided. [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 the inner part 7 and the gear component 8 26 Circular Web 27 Mounting part 28 Cylindrical part of mounting part 29 Outer seal portion of output element 15 30 Seals 31 Metal Core 32 Sealing element 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 element 43 Seal lip 44 Front gutter 45 Seal in output assembly

Claims

1. A strain wave gear comprising a first assembly (2) configured as a flanged bush (8) and provided with a flexible gear element (11) with external toothing (11) mounted thereon, a wave generator (16) provided for deforming the flexible gear element (8), and an output assembly (12) having internal toothing (14) meshing with the external toothing (11) of the flexible gear element (11), the output assembly (12) being supported by a rolling bearing (34) on the first assembly (2). ), the rolling bearing (34) being sealed on both sides by seals (30, 40) acting between the first assembly (2) and the output assembly (12), one of these two seals (40) 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 to the output assembly (12).

2. 2. The strain wave gear according to claim 1, characterized in that the seal (40) defining the lubricant space is arranged between an end face of the output assembly (12) and a collar (9) of the flexible gear element (8).

3. 3. A strain wave gear according to claim 2, characterized in that the seal (40) is configured as a contact seal which is in contact with the collar (9) and is effective on at least one side.

4. 4. The strain wave gear according to claim 3, wherein the seal (40) has a metal core (41) inserted in a front groove (44) of the output assembly (12).

5. 5. The strain wave gear according to claim 3 or 4, characterized by a third seal (25) opposite the seal (40) that contacts the collar (9) of the flexible gear element (8) and defines the lubricant space extending to the teeth (11, 14) of the flexible gear element (8) and the output assembly (12).

6. 6. A strain wave gear according to claim 5, characterized in that the third seal (25) is carried on the first housing assembly (2).

7. 7. The strain wave gear according to claim 1, wherein the output 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).

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

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

10. 10. 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 one of the seals (40) and extending to the teeth (11, 14) are filled with different lubricants.

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