Shaft drive

Abstract

A wave gear (1) comprises a first wave generator (22) configured to bring a toothed flexible gear element (5) partially into engagement with the teeth of a rigid gear element (9), thereby forming several separate engagement areas. Additionally, a second wave generator (29) exists, configured to keep the toothed flexible gear element (5) at a distance from the teeth of the rigid gear element (9) in areas outside the engagement areas.

Description

[0001] The invention relates to a wave gear, for example usable as an actuator, according to the preamble of claim 1.

[0002] Wave gears operate with an elastic toothed gear element that is continuously deformed during operation by a wave generator and, in moving areas, engages with the teeth of a rigid gear element. This latter gear element can be, in particular, an output element of the wave gear.

[0003] A wave gear of this type and a method for assembling a wave gear are known, for example, from DE 10 2018 102 774 B3. The known wave gear has a flexible, externally toothed gear element designed as a collar sleeve, i.e., having a hat shape. The flexible gear element interacts directly with an output element mounted in a housing of the wave gear. According to the teaching of DE 10 2018 102 774 B3, a spring ring is provided for axially supporting the output element on both sides in the housing. This spring ring engages in annular grooves of both the output element and the housing.

[0004] German patent DE 10 2023 108 432 A1 describes a method for detecting a faulty measuring channel in a strain wave drive, i.e., a wave drive. To detect a faulty measuring channel on an elastic transmission element of the wave drive, a strain gauge arrangement with multiple measuring channels is used, thus enabling plausibility checks. The detection method according to DE 10 2023 108 432 A1 can be applied, in particular, to a drive module of a robot arm.

[0005] Another wave gear with integrated sensors is disclosed in DE 10 2023 100 870 B4. In this case, the wave gear is part of a steering system for a motor vehicle. The sensors include a rotary angle sensor and a linear displacement sensor. Further wave gears are disclosed in DE 10 2021 132 229 A1 and DE 11 2012 000 058 B4.

[0006] 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 high operational reliability, is characterized by a particularly favorable ratio between the required installation space and the transmissible torques.

[0007] This problem is solved according to the invention by a wave gear with the features of claim 1. The wave gear comprises, in a basic concept known per se, a first wave generator which brings a toothed flexible gear element partially into engagement with a toothing of a rigid gear element and thus forms several separate engagement areas.

[0008] According to claim 1, the wave gear further comprises a wave generator which holds the toothed flexible gear element at a distance from the toothing of the said rigid gear element in areas outside the engagement areas.

[0009] This creates a forced gap between the different gear teeth in areas where the teeth of the various transmission elements—that is, the flexible transmission element on the one hand and the non-deformable transmission element on the other—should not mesh. Compared to conventional wave gears, sometimes also referred to as stress shafts, this allows for more precisely defined deformations of the elastic transmission element. This can be used, for example, to work with greater deformations of the elastic transmission element. It also improves the possibilities of creating more than two engagement areas, for example, three or four such areas, which, given the external dimensions, benefits the transmissible torque and wear resistance.In particular, by keeping the teeth of the elastic gear element away from the teeth of the rigid gear element outside the engagement areas with the help of the second wave generator, tooth grinding between the elastic gear element and the rigid gear element is avoided.

[0010] Each of the two wave generators can, in principle, include a rotary bearing of any design, for example, a rolling or plain bearing. For instance, both rotary bearings are designed as rolling bearings, specifically ball bearings. Alternatively, the rolling bearings of the wave generators can be designed as needle roller or roller bearings. The rolling elements of the bearings can roll either directly on the deformable gear element or on a separate deformable bearing component. The rolling elements of the different bearings are not necessarily dimensioned uniformly. For example, the rolling elements of the first rolling bearing are larger than the rolling elements of the second rolling bearing. It is also possible to provide a rolling bearing in one of the two wave generators and a plain bearing in the other.

[0011] According to one possible embodiment of the wave gear, the flexible gear element is designed as a collar sleeve, which has a cylindrical section toothed along part of its length and interacting directly with the rigid gear element, as well as a collar adjoining the cylindrical section and attached to a housing element. Here, the second wave generator, which separates the toothing of the flexible gear element from that of the rigid gear element, can engage a bearing section of the cylindrical section, with the bearing section extending from the toothed section of the flexible gear element towards the end face of the cylindrical section opposite the collar.

[0012] The two wave generators can form an assembly comprising two interconnected rotating elements, one belonging to the first wave generator and the other to the second. It is also possible for at least one element to exist that is part of both the first and the second wave generator.

[0013] Several possible configurations provide for the inherently rigid gear element, which interacts directly with the flexible gear element, to be rotatably mounted by means of a rolling bearing. In this configuration, a cylinder circumscribing the second shaft generator can be arranged radially outside the first shaft generator, but radially inside the rolling elements, in particular cylindrical rollers, of the rolling bearing provided for supporting the inherently rigid gear element. The aforementioned rolling bearing is specifically designed to absorb radial forces, axial forces, and tilting loads. For example, it is a double-row angular contact roller bearing.

[0014] The wave gear can optionally be equipped with sensors, for example, for measuring forces and / or torques. The two wave generators are driven by a single electric motor. The wave gear can be configured as a high-reduction gearbox for use in vehicles or for industrial applications, such as robotics.

[0015] An embodiment of the invention is explained in more detail below with reference to a drawing. This drawing shows: Fig. 1. Partial view of a wave gear with two wave generators in a simplified sectional view.

[0016] In this case, a wave gear 1 is designed as an actuator suitable for use in an industrial robot. Regarding the basic design and function of wave gears, reference is made to the aforementioned prior art.

[0017] A housing element 2 of the wave gear 1 is connected, for example, to a first robot arm or to a rigid surrounding structure and comprises two housing parts 3 and 4. In the exemplary embodiment, a flexible gear element 5 of the wave gear 1 is designed as a collar sleeve. A collar 19, that is, an annular disc-shaped section of the flexible gear element 5, transitions at its outer edge into a mounting flange 6, which is suitable for screwing onto the housing element 2. For this purpose, the housing parts 3 and 4, as well as the mounting flange 6, have bores 7. A static seal 8 is inserted between the housing part 3 and the mounting flange 6.

[0018] The flexible gear element 5 interacts with an output-side, inherently rigid gear element 9 in a manner explained in more detail below. The gear element 9 is mounted in the housing element 2 by means of a rolling bearing 10, namely a double-row cylindrical roller bearing. The rolling bearing 10 is designed as an angular contact roller bearing in an X-arrangement. This means that imaginary pressure lines passing through its rolling elements 11, i.e., rollers, intersect in the shape of an X. The central axis of the wave gear 1 is designated MA.

[0019] A first row of rolling elements 11 rolls, as if from Fig. The rolling elements 11, as shown in section 1, roll on the first housing part 3, while a second row of rolling elements 11 rolls on the second housing part 4. The housing parts 3 and 4 thus represent bearing rings of the rolling bearing 10. The rolling elements 11 are located in the Fig. In the case outlined in 1, the gear element is guided in a cage 12. A dynamic seal 13 is arranged between the rotating, rigid gear element 9 and the housing element 2.

[0020] The rolling bearing 10 further comprises a bearing component 14, which is part of the output-side gear element 9. The bearing component 14 is rigidly connected to a toothed component 15, which is another part of the output-side gear element 9. For connecting the two parts 15 and 14, these have bores 16 and threaded bores 17, respectively. A seal 18 is inserted between the parts 14 and 15, that is, between the bearing component 14 and the annular, internally toothed component 15.

[0021] The flexible, externally toothed gear element 5, whose collar 19 is attached to the housing element 2, has a cylindrical section 20 adjoining the collar 19. A region of the cylindrical section 20 immediately adjoining the collar 19 is designed as a deformable area without teeth. A toothed section 21 of the cylindrical section 20 adjoins this non-toothed area.

[0022] The gear section 21 is brought into a shape that changes continuously during operation of the wave gear 1 by a first wave generator 22. The design and function of the first wave generator 22 are fundamentally adopted from wave gears as described in the prior art, including in the introductory description section of this document.

[0023] The first wave generator 22 has a rotating element 23. The axis of rotation of the element 23 is identical to the central axis MA. An electric motor (not shown), in particular a synchronous motor, is used to drive the rotating element 23. The outer contour of the rotating element 23 is not circular. Rather, in the exemplary embodiment, the outer contour of the rotating element 23 has four diameter maxima and four diameter minima located between these maxima. Alternatively, there could, for example, be two or three diameter minima and maxima.

[0024] A rolling bearing 24 of the first shaft generator 22 is mounted on the rotating element 23, which in this case—to exaggerate the point—has the shape of a square with rounded corners. The rolling bearing 24, in this case a ball bearing, has a flexible inner ring 25 that fully contacts the non-circular outer contour of the rotating element 23. Balls 26 roll on the inner ring 25 as the rolling elements of the rolling bearing 24. Alternatively, the outer circumferential surface of the rotating element 23 could be designed as a raceway on which the balls 26 roll. The balls 26 are guided in a cage 27, for example, a ball snap cage.

[0025] Furthermore, the rolling bearing 24 has an outer ring 28 whose shape permanently adapts to the non-circular shape of the rotating element 23. The outer ring 28 contacts the inner circumferential surface of the toothed section 21 without being rigidly connected to the flexible gear element 5. Analogous to the possible omission of the inner ring 25, a modified design (not shown) allows the balls 26 to roll directly on the inner circumferential surface of the cylindrical section 20 of the flexible gear element 5.

[0026] The non-circular shape of the rotating element 23 ensures that the external teeth of the gear section 21 provided by the flexible gear element 5 engage with the internal teeth of the output-side, rigid gear element 9 only in four engagement areas, which are uniformly distributed around the circumference of the gear section 21. Depending on the contour of the rigid gear element 9, a different number of engagement areas may also exist. In particular, corresponding to the previously discussed number of diameter maxima of the rotating element 23, there may only be three or two engagement areas in which a torque is transmitted from the flexible gear element 5 to the output-side gear element 9.In any case, a slightly different number of teeth on the external teeth of the gear section 21 on the one hand and on the internal teeth of the output-side, rigid gear element 9 - more precisely: on the other hand, the internal teeth of the toothed component 15 which does not have a direct rolling bearing function - ensures that a full revolution of the rotating, electrically driven element 23 is converted into a comparatively small pivoting motion between the housing element 2 and the output-side gear element 9.

[0027] In addition to the first wave generator 22, there is a second wave generator 29, which is also referred to as the internal wave generator. Unlike the first wave generator 22, the second wave generator 29 does not force defined areas of the cylindrical section 20 of the flexible gear element 5 outwards, but inwards. For this purpose, the cylindrical section 20 is extended axially beyond the gear section 21, with the extension forming a support section 30 for the second wave generator 29.

[0028] A rotating element 31 of the second wave generator 29 is arranged coaxially to the rotating element 23 of the first wave generator 22 and is firmly connected to this rotating element 23 in a manner not shown, whereby a one-piece design of the elements 23, 31 is also possible.

[0029] In the exemplary embodiment, an inner section 32 of the rotating element 31 rests flat on the rotating element 23. An annular-disc-shaped section 33 adjoins the outer edge of the inner section 32. The annular-disc-shaped section 33, in turn, transitions at its outer edge into a sleeve-shaped section 34.

[0030] The sleeve-shaped section 34 accommodates a rolling bearing 35 of the second shaft generator 29, which is also designed as a ball bearing. An inner ring 36 of the rolling bearing 35 rests on the support section 30 of the cylindrical section 20 of the flexible gear element 5. In an alternative embodiment, balls 37, i.e., rolling elements of the ball bearing 35, could roll directly on the support section 30. As shown in the Fig. As can be seen from Figure 1, the balls 37 of the second wave generator 29 have a smaller diameter than the balls 26 of the first wave generator 22. The balls 37 of the second wave generator 29 can also be guided in a cage (not shown). Alternatively, instead of the rolling bearing 35, the second wave generator 29 could be mounted in a sliding bearing.

[0031] The rolling bearing 35 in the exemplary embodiment has an outer ring 38 which is inserted into the sleeve-shaped section 34 of the rotating element 31. In a modified embodiment, the balls 37 roll directly on the inner circumferential surface of the sleeve-shaped section 34. In each case, the rolling element raceway on which the balls 37 roll has a shape that deviates from a circular form. Analogous to the outer circumferential surface of the rotating element 23, which is associated with the first shaft generator 22, the inner circumferential surface of the sleeve-shaped section 34 also describes a closed curve with four minima and four maxima. In the previously mentioned designs, which are also feasible, with three or two diameter maxima and minima respectively, the rotating element 31, which is associated with the second shaft generator 29, also has three or two diameter maxima and minima, respectively.

[0032] As from Fig. As can be seen from Figure 1, the outer diameter of the second wave generator 29 is larger than the diameter of the inner wave generator 22 given by the outer ring 28. At the same time, the complete second wave generator 29 is arranged radially inside the rolling elements 11, namely cylindrical rollers, of the rolling bearing 10, which is provided for supporting the rigid transmission element 9.

[0033] In the exemplary embodiment with four engagement areas between the flexible gear element 5 and the output-side, rigid gear element 9, there are, corresponding to the number of engagement areas, also four uniformly distributed areas around the circumference of the cylindrical section 20 in which the teeth of the flexible gear element 5 are disengaged from the internal teeth of the component 15. The disengagement of the cylindrical section 20 from the internal teeth of the component 15 belonging to the output-side gear element 9 is enforced by the second shaft generator 29. For this purpose, the minimum diameters of the inner circumferential surface of the sleeve-shaped section 34 are each arranged centrally between two maximum diameters of the rotating element 31. Reference symbol list 1 wave gear 2 Housing element 3 Housing part 4 Housing part 5 flexible gear element 6 Mounting flange 7 bore 8 Seal, static 9 output-side, inherently rigid gear element 10 rolling bearings, double-row cylindrical roller bearing 11 rolling elements, roller 12 cage 13 Dynamic seals 14 Bearing component, part of the output-side gear element 15 toothed component, part of the output-side gear element 16 bore 17 threaded holes 18 Seal, static 19 annular disc-shaped section of the flexible gear element, collar 20 cylindrical section of the flexible gear element 21 Gear section of the flexible gear element 22 first wave generator 23 rotating element of the first wave generator 24 rolling bearings of the first shaft generator, ball bearings 25 inner ring 26 rolling elements, ball 27 cage 28 Outer ring 29 second wave generator 30 Support section of the flexible gear element 31 rotating element of the second wave generator 32 inner section 33 ring-shaped section 34 sleeve-shaped section 35 rolling bearings of the second shaft generator, ball bearings 36 inner ring 37 rolling elements, ball 38 Outer ring MA Central Axis

Claims

Wave gear (1), comprising a first wave generator (22) which is configured to bring a toothed flexible gear element (5) partially into engagement with a toothing of a rigid gear element (9) and thus to form several separate engagement areas, characterized by a second wave generator (29) which is configured to keep the toothed flexible gear element (5) at a distance from the toothing of the rigid gear element (9) in areas outside the engagement areas. Wave gear (1) according to claim 1, characterized in that the first wave generator (22) comprises a first rolling bearing (24). Wave gear (1) according to claim 1 or 2, characterized in that the second wave generator (29) comprises a second rolling bearing (35). Wave gear (1) according to claims 2 and 3, characterized in that the rolling elements (26) of the first rolling bearing (24) are larger than the rolling elements (37) of the second rolling bearing (35). Wave gear (1) according to one of claims 1 to 4, characterized in that the flexible gear element (5) is designed as a collar sleeve which has a cylindrical section (20) toothed on part of its length and a collar (19) adjoining the cylindrical section (20) and attached to a housing element (2). Wave gear (1) according to claim 5, characterized in that the second wave generator (29) engages a support section (30) of the cylindrical section (20), wherein the support section (30) extends from the toothed section of the flexible gear element (5) which interacts directly with the rigid gear element (9) in the direction of the end face of the cylindrical section (20) opposite the collar (19). Wave gear (1) according to one of claims 1 to 6, characterized in that the first wave generator (22) comprises a rotating element (23) which is rigidly connected to a rotating element (31) of the second wave generator (29). Wave gear (1) according to one of claims 1 to 7, characterized in that more than two engagement areas are formed on the circumference of the flexible gear element (5) and the inherently rigid gear element (9). Wave gear (1) according to one of claims 1 to 8, characterized in that the inherently rigid gear element (9) which interacts directly with the flexible gear element (5) is rotatably mounted by means of a rolling bearing (10). Wave gear (1) according to claim 9, characterized in that a cylinder circumscribing the second wave generator (29) is arranged radially outside the first wave generator (22), but radially inside the rolling elements (11) of the rolling bearing (10), which is provided for supporting the inherently rigid gear element (9).

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