Shaft drive

Abstract

A wave gear (1) comprises a wave generator (2) and a flexible gear element (3) deformable by means of the wave generator (2), which is attached to a housing element (4) and interacts directly with an output element (6). The flexible gear element (3) includes an annular disk-shaped connecting section (7) attached to the housing element (4), a relatively thin-walled base (10) extending from the connecting section (7), which has a single-layer section (11) and a multi-layer section (12), and a toothed section (13) adjoining the multi-layer section (12) of the base (10).

Description

[0001] The invention relates to a wave gear suitable, for example, for use in an industrial robot, according to the preamble of claim 1.

[0002] A wave gear of this type is known, for example, from DE 10 2021 132 229 A1. The known wave gear has a flexible gear element shaped like a collar sleeve, which is attached to a housing of the wave gear. A wave generator of the wave gear according to DE 10 2021 132 229 A1, designed to deform the flexible gear element, is electrically driven via a shaft. This shaft is supported in the housing by a deep groove ball bearing with four-point contact. An output element of the known wave gear is supported in the housing of the wave gear by means of a double-row angular contact roller bearing.

[0003] Further wave gears that can be used as actuators in industrial robots are disclosed, for example, in documents DE 10 2022 102 500 A1, DE 10 2022 128 419 A1 and DE 10 2020 118 797 A1. In the latter case, a rolling element raceway of a wave generator, which includes a rolling bearing designed as a roller bearing, can be formed either directly by a flexible gear element or by a separate bearing ring.

[0004] The invention is based on the objective of providing a wave gear that is further developed compared to the aforementioned prior art and which, with compact external dimensions and a manufacturing-friendly design, is characterized by particularly high mechanical load capacity and durability.

[0005] This problem is solved according to the invention by a wave gear designed as a reduction gear, particularly suitable for use as an actuator of an industrial robot, with the features of claim 1.

[0006] The wave gear comprises, in a basic concept known per se, a wave generator and a flexible, toothed gear element deformable by means of the wave generator, which is attached to a housing element of the wave gear and interacts directly with an output element of the wave gear arranged concentrically to the wave generator.

[0007] According to claim 1, the flexible gear element comprises an annular disc-shaped connecting section attached to the housing element of the wave gear, a comparatively thin-walled base extending from the connecting section, which has a single-layer section and a multi-layer section, and a toothed section adjoining the multi-layer section of the base.

[0008] With its partially multi-layered base, the flexible gear element thus describes a partially folded shape. The number of layers in the multi-layered section is not subject to any theoretical limitations. In an extreme case, if a large number of layers are present, a section of the flexible gear element can be shaped like a bellows. In any case, the partially multi-layered design of the base of the flexible gear element benefits the deformability of this element while maintaining compact external dimensions. At the same time, the flexible gear element is capable of absorbing supporting moments.

[0009] Compared to the base of the flexible gear element, the annular connecting section, which abuts the outer edge of the base, is thick-walled and practically non-deformable. In particular, the wall thickness of the base of the flexible gear element is less than half the wall thickness of the connecting section. This relationship applies, among other things, to variants of the wave gear where the total thickness of the multi-layered section is less than the wall thickness of the connecting section. The total thickness of the multi-layered section is defined here as the sum of the base wall thickness multiplied by the number of layers and the total width of the spaces between these layers.

[0010] Several possible embodiments of the wave gear provide for the multi-layered section to be designed as a two-layered section, with the distance between the two layers of said section being at least twice the wall thickness of the base. Deformations of the flexible gear element are absorbed by both the single-layered and the two-layered sections. Frictional contact between the individual layers of the two- or multi-layered section is not intended under any operating condition.

[0011] A radius of curvature formed in the multi-layered section, particularly in the two-layered section, between parallel, spaced-apart layers of the base can be larger than a radius of curvature formed at the transition between the multi-layered base and the toothed section of the flexible gear element. Specifically, a radius of curvature at the inner edge of the flexible gear element at the transition between the two layers of the base is larger than a radius of curvature at the transition between one of these two layers and the toothed section of the flexible gear element. In this way, unintended contact between individual layers of the base is prevented while maintaining considerable deformation reserves, with deformations of the flexible gear element occurring particularly in its base.The toothed section, also in other embodiments of the wave gear, has in particular a sleeve shape concentric to the central axis of the wave gear, wherein it is provided with an external toothing that meshes with an internal toothing of the output element.

[0012] The radial dimension of the multi-layer section of the flexible gear element, and thus of the entire wave gear, is, for example, at least half and at most one and a half times the dimension of the single-layer section of the base measured in the same direction. The connecting section is not considered part of the single-layer section of the base. A transition section with a wall thickness decreasing radially inwards may be formed between the connecting section and the single-layer section of the base. Alternatively, an annular step may be formed between the connecting section and the single-layer section.

[0013] The total thickness of the flexible gear element, measured in the axial direction of the shaft generator, is, for example, at least one-quarter and at most three-quarters of the total thickness of the flexible gear element measured radially between the outer edge of the connection section and the inner edge of the base, i.e., at a transition between two layers of the base. The inner edge of the base defines a cylinder, which specifies the inner diameter of the flexible gear element. This total thickness of the flexible gear element corresponds to half the difference between the outer diameter measured at the outer edge of the connection section and the inner diameter of the flexible gear element.

[0014] The wave generator can, in principle, have either a plain bearing or a rolling bearing. In the case of a rolling bearing, the centers of the rolling elements, in particular balls, of the rolling bearing can be arranged on an ellipse that lies outside the cylinder described by the inner edge of the base.

[0015] A further rolling or sliding bearing is provided for supporting the output element within the housing element. Particularly when this bearing is designed as a rolling bearing, it can extend beyond the flexible gear element in exactly one axial direction. The rolling bearing is, for example, a double-row angular contact roller bearing which, viewed radially from the bearing and thus from the entire wave gear, is located partly within the connection section and partly within the single-layer section of the base, but outside the multi-layer section. In this configuration, one row of the rolling elements of the angular contact roller bearing can be located entirely within the annular space in which the flexible gear element is inscribed, whereas each rolling element of the second row is located partly within and partly outside this space.

[0016] The wave gear is suitable not only for use in industrial robots, but also, for example, as an actuator for mobile applications. In particular, an electric drive for the wave gear is provided.

[0017] An embodiment of the invention is explained in more detail below with reference to a drawing. This drawing shows: Fig. 1. A section of a wave gear in a sectional view.

[0018] A wave gear unit, designated by reference numeral 1, is intended for use as an actuator in an industrial robot (not shown). Regarding the basic design and function of wave gear unit 1, reference is made to the prior art cited above.

[0019] The wave gear 1 comprises a wave generator 2, which is designed to deform a flexible gear element 3 of the wave gear 1. The flexible gear element 3 is designed as a modified collar sleeve and is attached to a housing element 4 of the wave gear 1. An output element 6 of the wave gear 1 is mounted in the housing element 4 by means of a rolling bearing 5, which in this case is designed as a double-row angular contact roller bearing. In the arrangement according to Fig. 1 The central axis of the wave gear 1 is located in a vertical orientation to the right of the components of the wave gear 1 shown.

[0020] The flexible gear element 3 has the basic shape of a ring, the radially outer edge of which is formed by an annular connecting section 7, which is attached to the housing element 4. A seal inserted between an end face of the housing element 4 and the connecting section 7 is designated 8. An annular step 9 is formed on the inner edge of the annular connecting section 7. The wall thickness of the connecting section 7, measured in the axial direction of the wave gear 1, is designated d7. At the annular step 9, the connecting section 7 transitions into a base 10, which has a thinner wall than the connecting section 7. The wall thickness of the base 10 is designated d10 and is less than half, and in this embodiment less than a quarter, of the wall thickness d7 of the connecting section 7.

[0021] The base 10 comprises a single-layer section 11 directly formed onto the connecting section 7, and a multi-layer section 12, which in the exemplary embodiment is two-layered. The total thickness of the multi-layer section 12, measured in the axial direction, is designated H12 and is less than the wall thickness d7 of the connecting section 7.

[0022] A sleeve-shaped, toothed section 13 of the flexible gear element 3 adjoins the two-layer section 12. Viewed in the radial direction of the flexible gear element 3, the toothed section 13 marks the boundary between the single-layer section 11 and the multi-layer section 12. The single-layer section 11 is located radially outside and the multi-layer section 12 radially inside the toothed section 13. The external toothing of the latter section 13 is designated 14.

[0023] The multi-layered section 12 of the flexible gear element 3 comprises a first layer 15, which is a continuation of the single-layer section 11, and a second layer 16 spaced parallel to the first layer 15. The two layers 15 and 16 are connected to each other by a curved section 17 of the base 10. Another curved section, designated 18, is formed between the second layer 16 and the essentially cylindrical toothed section 13. R17 and R18 are the radii of curvature of the curved sections 17 and 18, respectively, measured on the outside of the respective curvature. As shown in Fig. As can be seen from Figure 1, the radius of curvature R17, which is formed within the multilayer section 12, is larger than the radius of curvature R18 formed between the multilayer section 12 and the toothed section 13. By definition, both curvature regions 17 and 18 are attributed to the multilayer section 12. In the exemplary embodiment, the radial width of the multilayer section 12, designated B12, is at least 5% and at most 35% larger than the width of the single-layer section 11, designated B11, which is measured in the same direction. This applies to the configuration according to Figure 1. Fig. 1, in which the toothing 14 of the flexible gear element 3 designed as a modified collar sleeve engages with a toothing 19 of the rigid output element 6.

[0024] The wave generator 2 comprises a ball bearing as a rolling bearing 20. An inner ring 22 is located on a driven shaft 21, which has an elliptical, non-circular cross-section. The rolling elements, i.e., balls, of the rolling bearing 20, designated 23, roll on this inner ring. In the exemplary embodiment, the rolling elements 23 of the rolling bearing 20, i.e., the ball bearing, are guided in a cage 24. The outer ring 25 of the rolling bearing 20 continuously adapts to the non-circular shape of the shaft 21 and the inner ring 22. In this way, the teeth 14 of the flexible gear element 3 engage with the teeth 19 of the output element 6 at two diametrically opposed points, while the teeth 14 and 19 are separated from each other in all other circumferential regions.A slightly different number of teeth in the various gears 14 and 19 ensures, in a manner known per se, that a full rotation of the shaft 21 is converted into a comparatively small pivoting of the output element 6. The wave gear 1 thus functions as a high-reduction actuator.

[0025] During the rotation of the shaft 21, deformations of the toothed section 13 occur mainly in the radial direction. The base 10 is simultaneously subject to more complex deformation processes. In the exemplary embodiment, the wall thickness d10 of the base 10 is at least largely uniform. The distance h12 between the two layers 15, 16 of the multilayered section 12 of the base 10 is subject to operational fluctuations, but is at least twice the wall thickness d10 of the base 10 in every operating condition.

[0026] The rolling bearing 5, in which the output element 6 is mounted in the housing element 4, comprises two rows 26, 27 of rolling elements 28, namely cylindrical rollers. The cylindrical rollers 28 of each row of rolling elements 26, 27 are guided in a cage 29 and, in the exemplary embodiment, roll on rolling element raceways 30, 31, which are formed directly by the housing element 4 and the output element 6, respectively. Alternatively, separate bearing rings could be provided. The rolling bearing 5 is capable of accommodating radial loads, axial loads, and tilting loads. A dynamic seal 32, designed as a contact seal, is also arranged between the housing element 4 and the output element 6. The seal 32 comprises a metallic core 33, a sealing lip 34 that contacts the output element 6, and a spring 35 that applies a force to the sealing lip 34.

[0027] The in Fig. The visible cross-section of the flexible gear element 3 occupies more space in the radial direction of the wave gear 1 than in the axial direction. The total thickness of the flexible gear element 3, measured in the axial direction of the wave generator 2 and thus of the entire wave gear 1, is denoted by H3. GS denotes the total thickness of the flexible gear element 3, measured radially between the outer edge of the connecting section 7 and the inner edge of the base 10 – more precisely, the curvature region 17. The inner diameter of the flexible gear element 3 corresponds to the difference between the outer diameter of the gear element 3 and twice the total thickness GS.

[0028] An annular disk-shaped space is defined by a cylinder circumscribing the outer edge of the connecting section 7, a cylinder inscribed in the flexible gear element 3 and contacting the curvature region 17, and two mutually parallel planes axially aligned with the gear element 3. The gear element 3 is completely arranged within this annular disk-shaped space. The first row 26 of rolling elements 28, i.e., cylindrical rollers, of the double-row rolling bearing 5 is located completely within the annular disk-shaped space. In contrast, each rolling element 28 of the second row 27, as shown in the diagram, is located outside the annular disk-shaped space. Fig. 1, partially inside and partially outside the annular space defined as described. This means that the rolling bearing 5 aligns the flexible gear element 3 in exactly one axial direction, in the arbitrary positioning according to Fig. 1 point downwards, towering above.

[0029] What's next? Fig.As can be seen from Figure 1 in conjunction with the explanations above relating to the wave generator 2, the centers of the rolling elements 23, i.e., balls, of the rolling bearing 20, which is part of the wave generator 2, are located on an ellipse that lies outside the cylinder defined by the inner edge of the base 10. This ellipse is thus completely enclosed within the annular space in which the flexible gear element 3 is located. The resulting radial overlap between the wave generator 2 and the flexible gear element 3 allows for a space-saving design of the wave gear 1, while simultaneously keeping the local deformations that the flexible gear element 3 experiences continuously during normal operation within a range that minimizes material wear. Reference symbol list 1 wave gear 2-wave generator 3 flexible gear element 4 Housing element 5 rolling bearings 6 Output element 7 Connection section 8 Seal Level 9 10 Floor 11 single-layer section 12 multi-layered section 13 toothed section 14 gear teeth 15 first layer 16 second layer 17 Curvature range 18 Curvature range 19 Interlocking 20 rolling bearings 21st wave 22 inner ring 23 rolling elements, ball 24 cage 25 outer ring 26 rolling element row 27 rolling element row 28 rolling elements, cylindrical roller 29 cage 30 rolling element raceway 31 Rolling element raceway 32 Seal 33 core 34 Sealing lip 35 spring B11 Width of the single-layer section 11 B12 Width of the multilayer section 12 d7 Wall thickness of connection section 7 d10 Wall thickness of the floor 10 GS Total strength of the flexible gear element 3 h12 Distance between layers 15, 16 H12 Total thickness of the multilayer section 12 H3 Total thickness of the flexible gear element 3 R17 radius of curvature R18 radius of curvature QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2021 132 229 A1

[0002] DE 10 2022 102 500 A1

[0003] DE 10 2022 128 419 A1

[0003] DE 10 2020 118 797 A1

[0003]

Claims

[1] Wave gear (1), comprising a wave generator (2) and a flexible gear element (3) which can be deformed by means of the wave generator (2) and which is attached to a housing element (4) and interacts directly with an output element (6), characterized by , that the flexible gear element (3) comprises an annular disc-shaped connecting section (7) attached to the housing element (4), a comparatively thin-walled base (10) extending from the connecting section (7), which has a single-layer section (11) and a multi-layer section (12), and a toothed section (13) adjoining the multi-layer section (12) of the base (10). [2] Wave gear (1) according to claim 1, characterized by , that the wall thickness (d10) of the base (10) of the flexible gear element (3) is less than half the wall thickness (d7) of the connecting section (7). [3] Wave gear (1) according to claim 2, characterized by, that the total thickness (H12) of the multilayer section (12) is less than the wall thickness (d7) of the connecting section (7). [4] Wave gear (1) according to any one of claims 1 to 3, characterized by , that the multi-layered section (12) is designed as a two-layered section, wherein the distance (h12) between the two layers (15, 16) of said section (12) is at least twice the wall thickness (d10) of the base (10). [5] Wave gear (1) according to claim 4, characterized by , that a radius of curvature (R17) at the transition between the two layers (15, 16) of the base (10) is larger than a radius of curvature (R18) at the transition between one of these two layers (16) and the toothed section (13) of the flexible gear element (3). [6] Wave gear (1) according to any one of claims 1 to 5, characterized by, that the width (B12) of the multilayer section (12) in the radial direction of the flexible gear element (3) is at least half and at most 1.5 times the width (B11) of the single-layer section (11) of the base (10) of the flexible gear element (3) measured in the same direction. [7] Wave gear (1) according to any one of claims 1 to 6, characterized by , that the total thickness (H3) of the flexible gear element (3) to be measured in the axial direction of the wave generator (2) shall be at least one quarter and at most ¾ of the total thickness (GS) of the flexible gear element (3) to be measured in the radial direction between the outer edge of the connection section (7) and the inner edge of the base (10). [8] Wave gear (1) according to claim 7, characterized by, that the wave generator (2) comprises a rolling bearing (20) wherein the centers of its rolling elements (23) are arranged on an ellipse which lies outside a cylinder described by the inner edge of the base (10). [9] Wave gear (1) according to any one of claims 1 to 8, characterized by , that the output element (6) which interacts directly with the flexible gear element (3) is mounted in the housing element (4) by means of a rolling bearing (5) which extends beyond the flexible gear element (3) in exactly one axial direction. [10] Wave gear (1) according to claim 9, characterized by , that the rolling bearing (5) is designed as a double-row angular contact roller bearing and - viewed in the radial direction - is arranged partly in the area of ​​the connecting section (7) and partly in the area of ​​the single-layer section (11) of the base (10), but outside the multi-layer section (12).

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