Strain wave gear and method for operating a strain wave gear

Abstract

A strain wave gear (1), in particular in an industrial robot, comprises a wave generator (16), a flexible, externally toothed transmission element (8), an internally toothed output element (7), and a lubricant chamber (25), wherein a lubricant conveying structure (31) is formed on an inner circumferential surface (26) of the output element (7), said inner circumferential surface delimiting the lubricant chamber (25).

Description

[0001] Corrugated gears and methods for operating a corrugated gear

[0002] The invention relates to a wave gear constructed according to the preamble of claim 1, particularly suitable for use in an industrial robot. The invention further relates to a method for operating a wave gear.

[0003] A wave gear of this type is known, for example, from DE 10 2022 100 356 B3. The known wave gear comprises a first assembly to which a flexible gear element designed as a collar sleeve is attached. The known wave gear further comprises a wave generator for deforming the flexible gear element, as well as an output-side assembly having internal teeth meshing with external teeth of the flexible gear element. A lubricant chamber formed within the wave gear is delimited, among other things, by a seal arranged between the aforementioned assemblies.

[0004] Another wave gear, which has a flexible gear component in the form of a collar sleeve, is known from DE 10 2016 207 612 A1. The collar sleeve of this wave gear is at least indirectly attached to an surrounding component. A rigid gear component, which functions as the output element of the wave gear and interacts directly with the flexible gear component, is rotatably arranged in the surrounding component. Static seals are located at various points in the wave gear according to DE 10 2016 207 612 A1.

[0005] Various embodiments of wave gears, in which a collar sleeve is attached to an assembly that is rotatable as a whole, are known, for example, from documents DE 10 2018 128 930 A1, WO 2017 / 206988 A1, and DE 10 2017 128 423 A1. In these three cases, the wave gears are located in electromechanical camshaft adjusters. DE 10 2017 119 461 B4 discloses a rolling bearing designed as a deep groove ball bearing for a wave gear. An inner ring of this rolling bearing has an inner ring with an elliptical circumferential contour. A seal is arranged between the inner ring and the outer ring of the rolling bearing, which is supported against rotation on the inner ring and bears against the outer ring with an elliptical circumferential contour.

[0006] A manipulator arm for a robot is known from DE 10 2020 107 990 A1. The manipulator arm is adjustable by means of a printed circuit board motor and a gearbox, the gearbox being designed as a wave gear, cycloidal gear or planetary gear.

[0007] The invention is based on the objective of further developing wave gears, which are suitable for use in an industrial robot, for example, and are compact and easy to manufacture, compared to the prior art, particularly with regard to lubrication technology, with special attention paid to durability.

[0008] This problem is solved according to the invention by a wave gear with the features of claim 1. Likewise, the problem is solved by a method for operating a wave gear designed according to claim 9. The embodiments and advantages of the invention explained below in connection with the operating method also apply mutatis mutandis to the device according to the application, i.e., the wave gear, and vice versa.

[0009] The wave gear comprises, in a basic concept that is known in itself,

[0010] - a wave generator comprising a rotating part with a non-circular, in particular elliptical, outer contour and a rolling bearing, in particular in the form of a ball bearing, wherein the rolling elements of the rolling bearing are forced onto a non-circular path by the non-circular outer contour of the rotating part and thereby contact a flexible outer ring, - a flexible, externally toothed gear element surrounding the flexible outer ring of the wave generator,

[0011] - an internally toothed gear element meshing with the teeth of the flexible gear element, intended as an output element of the wave gear,

[0012] - a housing assembly to which the flexible gear element is held, and in which the internally toothed gear element is rotatably mounted by means of a rolling bearing, wherein a lubricant chamber is formed between the meshing teeth of the flexible gear element and the output element, a non-toothed outer circumferential surface of the flexible gear element, and an inner circumferential surface of the output element.

[0013] According to claim 1, a lubricant delivery structure is formed on the inner circumferential surface of the output element that delimits the lubricant chamber. The lubricant delivery structure can, for example, be in the form of a thread.

[0014] The invention is based on the consideration that lubrication is required at various points in a wave gear. Firstly, the interlocking gear teeth of a flexible and a rigid gear element must be lubricated. Secondly, the bearing between two elements that are rotatable relative to each other, in particular a housing element and an output element, also requires lubrication.

[0015] According to the teaching of the aforementioned patent specification DE 10 2022 100 356 B3, two chambers, in which the aforementioned gears or the bearing of a rotating part are located, are separated from each other by a contacting seal. In this way, it is possible to fill different chambers with different lubricants, which differ from each other, particularly with regard to their viscosity. As detailed in DE 10 2022 100 356 B3, a grease can be provided as the lubricant in a first lubricant chamber and an oil in the second lubricant chamber.

[0016] The application-specific solution deliberately departs from this known concept by providing a lubricant delivery structure outside the engagement area of ​​the externally toothed flexible gear element, which can be used to supply lubricant not only to the teeth of the flexible and the output-side gear element, but also to additional areas of the wave gear that are separated from the aforementioned teeth.

[0017] While the possibilities for separating different subvolumes for lubrication purposes are limited compared to DE 10 2022 100 356 B3, depending on the embodiment, this design offers good conditions for a compact wave gear construction while simultaneously providing good lubrication. Grease is particularly suitable as a lubricant. Alternatively, oil lubrication can be used.

[0018] The flexible gear element of the wave gear can be designed, in particular, as a collar sleeve. In this configuration, the lubricant chamber can extend from the teeth of the flexible gear element and the output element into an annular space with a sleeve-like basic shape. This annular space is bounded internally by a cylindrical section of the flexible gear element and externally by the inner circumferential surface of the output element, including the lubricant delivery structure. From this sleeve-shaped, i.e., essentially cylindrical, annular space, the lubricant chamber can extend further through an annular disk-shaped cavity, which is bounded on one side by an end face of the output element and on the other by a collar of the flexible gear element, to the rolling bearing of the internally toothed gear element.The lubricant reservoir can thus have a shape adapted to the form of the flexible gear element and extended towards the rolling bearing of the output element. The internally toothed gear element, which serves as the output element of the wave gear, can be constructed in one or more parts. In the latter case, the output element can include a support ring which provides at least one raceway for the rolling bearing on its outer side and simultaneously the lubricant delivery structure on its inner side. The term "rolling bearing" here refers to the mounting of the output element within the housing assembly. An internally toothed gear, also part of the output element, can be attached to the support ring and interacts directly with the flexible gear element.

[0019] The lubricant delivery structure, formed by the one- or multi-part output element and specifically describing a thread, delivers lubricant located between the flexible gear element and the output element. Depending on the direction of rotation of the output element relative to the gear element, the lubricant flows in one or the other axial direction of the output element and thus of the entire wave gear, while a tangential delivery effect may also occur. If the rotating part that actuates the wave generator and thus ultimately adjusts the output element is adjusted in different directions during various operating phases of the wave gear, this means that a lubricant flow is generated in different directions depending on the operating phase. This significantly contributes to the complete lubrication of all bearings and gear teeth of the wave gear.

[0020] The rolling bearing that supports the output element in the housing assembly can generally be designed as a single-row or multi-row bearing. In the latter case, it is in particular a double-row angular contact ball bearing or a double-row angular contact roller bearing. Such a bearing is suitable for simultaneously absorbing radial loads, axial loads, and tilting loads.

[0021] According to a possible further development, the wave gear has an additional lubricant delivery structure on the outer circumferential surface of the driving rotating part, which is part of the wave generator. Like the lubricant delivery structure of the output element, this additional lubricant delivery structure can also describe a thread, in this case an external thread. The additional lubricant delivery structure generates a lubricant flow that penetrates the rolling bearing of the wave generator in the axial direction. Further structures of the wave gear can be provided for the targeted delivery of the lubricant to the gear teeth of the flexible gear element and the output element. Overall, this can result in a meandering flow of lubricant through the wave gear, changing direction multiple times.In order to guide lubricants specifically through the rolling bearing of the wave gear, an inner ring of this rolling bearing mounted on the rotating part can overlap in its radial direction with the lubricant conveying structure provided by the rotating part.

[0022] The patented method for operating a wave gear, which comprises a wave generator, a flexible gear element deformable by means of the wave generator, and an output element rotatably mounted in a housing assembly by means of a rolling bearing, which interacts directly with a toothing of the flexible gear element, is generally characterized in that lubricant, in particular lubricating grease, is conveyed from the toothing of the flexible gear element to the rolling bearing of the output element by means of a lubricant conveying structure provided by the output element.

[0023] The wave gear is particularly suitable for use as a positioning gear in an industrial robot. Applications in vehicles are also possible, for example in electromechanical actuators, including chassis actuators.

[0024] An embodiment of the invention is explained in more detail below with reference to a drawing. This drawing shows:

[0025] Fig. 1 shows a wave gear in a sectional view.

[0026] A wave gear, designated with reference numeral 1, is used as an actuator in an industrial robot (not shown). Regarding the fundamental function of wave gear 1, reference is made to the prior art cited at the beginning.

[0027] The wave gear 1 comprises a housing assembly 2, which is rigidly connected to a robot arm (not shown) and includes several housing components 3, 4 that are rigidly connected to one another. Each housing component 3, 4 provides a rolling element raceway for a rolling bearing 5, which in this case is designed as a double-row angular contact roller bearing. Thus, the housing components 3, 4 are outer rings of the rolling bearing.

[0028] The rolling bearing 5 absorbs both radial and axial forces and serves to support an output element 7, which in this embodiment is a multi-part, internally toothed gear element. Components of the output element 7 are a carrier ring 12 and an internally toothed gear 13, i.e., a ring gear, attached to it. A static seal inserted between the carrier ring 12 and the ring gear 13 is designated 23. Fastening means for the rigid connection of the carrier ring 12 to the ring gear 13 are not shown. The carrier ring 12 forms the inner ring of the double-row rolling bearing 5. The output element 7 is connected to a further, adjustable robot arm or to an end effector of the robot.

[0029] The housing components 3 and 4 are firmly connected to each other, for example by a screw connection (not shown). Furthermore, a flexible gear component 8, designed as a collar sleeve, is connected to the housing components 3 and 4. The collar 9 of the flexible gear component 8 is attached to the housing component 4, with a static seal 6 being inserted between the housing component 4 and a non-deformable end ring 15, which is thicker than the rest of the gear component 8.

[0030] In its radially inwardly projecting area beyond the housing component 4, the collar 9 is at least slightly elastically deflectable. A cylindrical section 10 of the flexible gear component 8 adjoins the inner edge of the collar 9 and is also elastically deflectable. The cylindrical, sleeve-shaped section 10 has external teeth 11, which are spaced apart from the collar 9 and extend to the end face of the collar sleeve 8 opposite the collar 9. The external teeth 11 partially mesh with internal teeth 14 of the ring gear 13, which is part of the output element 7.

[0031] A wave generator 16 is provided to deform the flexible gear component 8 during operation of the wave gear 1. The wave generator 16 comprises a rotating part 17 in the form of a shaft with an elliptical, non-circular cross-section. The rotating part 17 is electrically driven (not shown). A thin, flexible inner ring 22 of a rolling bearing 21 is mounted onto the non-circular outer contour of the rotating part 17, which is an input-side element of the wave gear 1. Rolling elements 18, namely balls, which are guided in a cage 19, roll on the inner ring 22, i.e., the inner ring of the rolling bearing. No seal is provided for the rolling bearing 21, i.e., the ball bearing, of the wave gear 1.

[0032] The outer ring 20 of the rolling bearing 21, designated 20, is elastically compliant and conforms to the non-circular shape of the inner ring 22. This causes the external teeth 11 to engage with the internal teeth 14 at two diametrically opposed points, while the internal teeth 14 are otherwise disengaged from the external teeth 11. The portion of the sleeve-shaped section 10 with the external teeth 11 rests loosely on the outer ring 20. Slightly different numbers of teeth on the external teeth 11 and the internal teeth 14 ensure, in a known manner, that a full rotation of the shaft 17 is converted into only a slight pivoting motion between the housing assembly 2 and the output element 7.

[0033] A non-toothed outer circumferential surface 24 of the sleeve-shaped section 10 defines a cavity used as a lubricant chamber 25, which is further bounded by an inner circumferential surface 26 of the output element 7. Starting from the toothed sections 11, 14, the cavity 25 extends over the substantially cylindrical area formed between the at least approximately concentric surfaces 24, 26, and further over an annular space, which is bounded on one side by an end face 27 of the output element 7 and on the other side by the collar 9 of the flexible gear element 8, to the rolling bearing 5, by which the internally toothed gear element 7 is mounted in the housing assembly 2. A seal 28 is provided for the dynamic sealing of the rolling bearing 5. This seal has a metallic core 29 and a sealing lip 30 and is thus designed as a contact seal.

[0034] Lubricant flow is illustrated by arrows in Figure 1. Since the gear teeth 11, 14 are partially lifted from each other in every operating state of the wave gear 1, a flow of lubricant between the gear components 7, 8 in their axial direction is possible. To support the lubricant flow, a lubricant delivery structure 31, which has the form of a thread, is formed on the inner circumferential surface 26. In the embodiment shown in Figure 1, the lubricant delivery structure 31 extends over less than half of the axially measured extent of the inner circumferential surface 26. Alternatively, the lubricant delivery structure 31, which can be produced, for example, by machining the inner circumferential surface 26, could extend over further areas of the inner circumferential surface 26, in particular over the entire inner circumferential surface 26.

[0035] In addition to the lubricant delivery structure 31 of the output element 7, the exemplary embodiment includes a further lubricant delivery structure 32 provided by the rotating part 17 of the shaft generator 16. This latter lubricant delivery structure 32, which also describes a thread, is formed on the outer circumferential surface 33 of the rotating part 17 and is axially spaced from the inner ring 22. The inner diameter of the threaded lubricant delivery structure 32 corresponds at least approximately to the inner diameter of the inner ring 22, while the outer diameter of the same lubricant delivery structure 32 corresponds at least approximately to the outer diameter of the inner ring 22. Thus, there is a radial overlap between the inner ring 22 and the lubricant delivery structure 32.As further visualized in Figure 1, the lubricant flow, which is directed towards the rolling bearing 21 by means of the lubricant conveying structure 32 and at least partially penetrates it, is deflected after the rolling bearing 21 so that the lubricant reaches the gear teeth 11, 14 and from there into the lubricant chamber 25 and further to the rolling bearing 5, which is designed as an axial-radial bearing. The deflection of the lubricant between the rolling bearing 21, which is designed as a ball bearing, and the gear teeth 11, 14 is effected in particular by housing-fixed elements of the wave gear 1 (not shown). A lubricant-promoting effect is also achieved by operational permanent deformations of the flexible gear element 8.

[0036] In contrast to lubricant conveyance achieved through such deformations, which at most only has a defined conveyance direction to a minor extent, the lubricant conveyance structures 31, 32, which are in the form of threads, ensure that the lubricant to be distributed in the wave gear 1 is conveyed in a defined direction, in particular in the axial direction of the wave gear 1. Depending on the direction of rotation of the input-side rotating part 17, which causes the output element 7 to rotate in the opposite direction, lubricant is transported within the wave gear 1 either in one or the other axial direction, so that the entire wave gear 1 is completely supplied with one and the same lubricant without being divided into several compartments that need to be sealed from each other and lubricated in different ways.

[0037] List of reference signs

[0038] Wave gear

[0039] Housing assembly, first housing component, second housing component

[0040] rolling bearing

[0041] Static seal

[0042] Output element, internally toothed gear element, flexible gear element

[0043] Collar of the flexible gear component; cylindrical section of the flexible gear component

[0044] External gearing

[0045] carrier ring

[0046] ring gear

[0047] internal teeth

[0048] graduation ring

[0049] Wave generator

[0050] Rotating part, shaft

[0051] rolling elements

[0052] cage

[0053] outer ring

[0054] Roller bearings, ball bearings

[0055] inner ring of the ball bearing

[0056] Seal between parts 12, 13

[0057] External perimeter

[0058] cavity, lubricant chamber

[0059] Inner perimeter area

[0060] Front surface

[0061] Seal, dynamic metallic core

[0062] Sealing lip, lubricant delivery structure of the output element, lubricant delivery structure of the drive-side rotating part, outer circumferential surface

Claims

Patent claims 1. Wave gear (1 ), with - a wave generator (16) comprising a rotating part (17) with a non-circular outer contour and a rolling bearing (21), wherein the rolling elements (18) of the rolling bearing (21) are forced onto a non-circular path by the non-circular outer contour and thereby contact a flexible outer ring (20), - a flexible, externally toothed gear element (8) which surrounds the flexible outer ring (20), - an internally toothed gear element (7) meshing with the toothing (11) of the flexible gear element (8) and intended as an output element, - a housing assembly (2) to which the flexible gear element (8) is held, and in which the internally toothed gear element (7) is rotatably mounted by means of a rolling bearing (5), wherein between the teeth (11 , 14) of the flexible gear element (8) and the output element (7), a non-toothed outer circumferential surface (24) of the flexible gear element (8), and an inner circumferential surface (26) of the output element (7) a lubricant chamber (25) is formed, characterized in that a lubricant conveying structure (31) is formed on the inner circumferential surface (26) of the output element (7) which limits the lubricant chamber (25).

2. Wave gear (1 ) according to claim 1 , characterized in that the lubricant delivery structure (31 ) is in the form of a thread.

3. Wave gear (1 ) according to claim 1 or 2, characterized in that the flexible gear element (8) is designed as a collar sleeve.

4. Wave gear (1 ) according to claim 3, characterized in that the lubricant chamber (25) is separated from the toothing (11 , 14) of the flexible gear element (8) and the output element (7) by an annular space with a sleeve-like basic shape, which extends inwards by a cylindrical section (10) of the flexible gear element (8) and is bounded externally by the inner circumferential surface (26) of the output element (7) including the lubricant conveying structure (31), and extends further over an annular disk-shaped space which is bounded on one side by an end face (27) of the output element (7) and on the other side by a collar (9) of the flexible gear element (8) to the rolling bearing (5) of the internally toothed gear element provided as the output element (7).

5. Wave gear (1 ) according to one of claims 1 to 4, characterized in that the internally toothed gear element (7) comprises a support ring (12) which provides on the outside at least one raceway of the said rolling bearing (5) and at the same time on the inside the lubricant conveying structure (31 ), and additionally a gear attached to the support ring (12) designed as a ring gear (13) which interacts directly with the flexible gear element (8).

6. Wave gear (1 ) according to one of claims 1 to 5, characterized in that the rolling bearing (5) supporting the output element (7) in the housing assembly (2) is designed as a double-row angular contact bearing.

7. Wave gear (1 ) according to one of claims 1 to 6, characterized in that a further lubricant conveying structure (32) is formed on an outer circumferential surface of the rotating part (17).

8. Wave gear (1 ) according to claim 7, characterized in that the rolling elements (18) of the rolling bearing (21 ) of the wave generator (16) roll on an inner ring (22) which is placed on the rotating part (17) and overlaps in the radial direction of the rotating part (17) with its lubricant conveying structure (32).

9. Method for operating a wave gear (1) comprising a wave generator (16), a flexible gear element (8) deformable by means of the wave generator (16), and an output element (7) mounted in a housing assembly (2) by means of a rolling bearing (5), which interacts directly with a toothing (11) of the flexible gear element (8), wherein lubricant is conveyed from the toothing (11) of the flexible gear element (8) to the said rolling bearing (5) by means of a lubricant conveying structure (31) provided by the output element (7).

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