Transmission assembly and method for operating a transmission assembly

Abstract

A transmission assembly which can be used in particular in an actuating drive comprises a harmonic drive (2), a clutch (3) which is situated on the output side of the harmonic drive (2) and includes a clutch actuating mechanism (5), and an output shaft (7). An input-side shaft (6) of a wave generator (18) of the harmonic drive (2) is non-rotatably coupled to the output shaft (7) via the closed clutch actuating mechanism (5) when the clutch (3) is open at the same time as long as a braking torque acting on the output shaft (7) does not exceed a torque threshold value, whereas when the torque threshold value is exceeded, the clutch (3) is kept closed by means of the clutch actuating mechanism (5), which simultaneously releases the non-rotatable coupling between the input-side shaft (6) and the output-side shaft (7), whereby a power flow is produced between the input-side shaft (6) and the output-side shaft (7) via the harmonic drive (2).

Description

[0001] Gear arrangement and method for operating a gear arrangement

[0002] The invention relates to a gear arrangement comprising a wave gear. The invention further relates to a method for operating such a gear arrangement.

[0003] Wave gears are designed as reduction gears in various applications and generally feature an elastic toothed gear element that interacts with at least one other gear element. The gearing of a wave gear can be backlash-free. Thanks to their high torque density, wave gears are suitable for compact drive solutions with high loads. Depending on the design, the output shaft of a wave gear can rotate either in the same or opposite direction to the input shaft.

[0004] From DE 10 2017 110 678 B3, a wave gear is known which comprises an elastic gear element designed as a collar sleeve. The known wave gear comprises a wave generator with a ball bearing as a rolling bearing, wherein a cage of the rolling bearing is simultaneously designed as an axially effective locking element.

[0005] A wave gear described in DE 10 2019 102 264 A1 has an elastic gear element designed as a flex ring and provided with external teeth. Furthermore, the device according to DE 10 2019 102 264 A1 includes a non-switchable brake in the form of a friction brake.

[0006] A wave gear described in DE 10 2016 222 897 A1 provides for the transmission of torque via an Oldham coupling. An Oldham coupling is a compensating coupling, not a switchable coupling.

[0007] A wave gear disclosed in DE 10 2015 224 897 A1 has a cup-shaped elastic gear element. In this case, an internally rigid, toothed ring gear, with which an external toothing of the elastic gear element meshes, is also elastically suspended.

[0008] Various wave gears intended for use in robots are described, for example, in documents EP 0 514 829 B1 and EP 0 741 256 B1.

[0009] German patent DE 10 2021 119 597 A1 relates to a linear drive with two reduction stages. The linear drive is intended for use in robotics and includes overload protection, which can be designed as an actively switchable clutch.

[0010] Further information on wave gears can be found in the following publication:

[0011] “Precision Shaft Gear Unit Series RT”, Schaeffler Technologies AG & Co. KG, Schweinfurt, TPI 275 / de-DE / DE / 2022-10

[0012] The invention is based on the objective of further developing gear technology based on wave gears, which is particularly suitable for use in robots, compared to the aforementioned prior art, whereby in particular an adaptation to different operating conditions should be possible.

[0013] This problem is solved according to the invention by a transmission arrangement with the features of claim 1. Likewise, the problem is solved by a method for operating a transmission arrangement designed according to claim 8. The embodiments and advantages of the invention explained below in connection with the operating method also apply mutatis mutandis to the device, i.e., the transmission arrangement, and vice versa. The transmission arrangement according to the application comprises a wave gear, a coupling located on the output side of the wave gear including a coupling actuation mechanism, and an output shaft, wherein an input-side shaft of a wave generator of the wave gear is rotationally fixed to the output shaft via the closed coupling actuation mechanism when the coupling is simultaneously open, as long as a braking torque acting on the output shaft does not exceed a torque limit.In contrast, if the torque limit is exceeded, the clutch is held closed by the clutch actuation mechanism, which simultaneously releases the rotationally fixed coupling between the input and output shafts, thus establishing a power flow between the input and output shafts via the wave gear. To a lesser extent, if a speed difference exists, power can also be fed directly from the input shaft to the output shaft.

[0014] The clutch actuation mechanism thus has multiple functions: Firstly, it can establish and disengage a rotationally fixed connection between the input shaft and the output shaft. Secondly, the clutch actuation mechanism is used to actuate the clutch located on the output side of the wave gear, thereby selectively activating or deactivating the wave gear.

[0015] The wave gear of the gear arrangement according to the application comprises an elastic, toothed gear element, which is designed, for example, as a collar sleeve. A toothed section of the elastic gear element can mesh with a rigid toothed component, which is rigidly connected to a coupling element of the gear arrangement. The coupling is the device designed to establish a torsionally rigid connection between the output element of the wave gear and the output shaft of the entire gear arrangement.

[0016] The aforementioned gear component can be attributed to the output element of the wave gear. This element is mounted in the housing of the gear assembly, for example, by means of rolling bearings, whereby a double-row needle roller or ball bearing is particularly suitable as a rolling bearing, which is designed to absorb radial loads, axial loads and tilting loads.

[0017] The wave generator can, in principle, comprise a plain bearing or a rolling bearing. In the case of a rolling bearing, this can be designed, in particular, as a single-row bearing, for example, as a ball bearing. In any case, an inner ring of the bearing is rigid, whereas an outer ring of the rolling bearing is flexible. It is also possible to design the bearing ring in which a section of the flexible transmission element is directly formed by a bearing ring.

[0018] In principle, the gearbox assembly can include a wide variety of bearing types. Besides rolling and sliding bearings, for example in the form of hydrodynamic bearings, magnetic bearings are also conceivable.

[0019] Regarding the clutch actuation mechanism, one can draw on the generally known designs of latching overload clutches. In this context, reference is made to DE 10 2019 120 320 A1, which concerns a safety clutch for a robot joint. A characteristic feature of such clutches is that opening the clutch under overload is accompanied by a radial displacement between two elements belonging to the clutch.

[0020] The method for operating the gear arrangement according to the application is generally characterized by the fact that, in a first operating phase, the rotation of an input shaft is directly transmitted to an output shaft, and in a second operating phase, in which a higher braking torque acts on the output shaft compared to the first operating phase, the rotation of the input shaft is converted into a rotation of the output shaft via a wave gear designed as a reduction gear. The switching between the different operating phases can occur automatically depending on the braking torque of the output shaft. In particular, the switching can be forced by a clutch actuation mechanism which, in the first operating phase, rotatably couples the input shaft to the output shaft.

[0021] The input shaft of the gearbox assembly, like the output shaft, can be either a solid shaft or a hollow shaft. Optionally, the gearbox assembly can be equipped with a torque sensor.

[0022] An embodiment of the invention is explained in more detail below with reference to a drawing. The drawing shows, in part schematically:

[0023] Fig. 1 shows a gear arrangement including a wave gear that can be automatically engaged as a reduction gear in a sectional view,

[0024] Fig. 2 is a diagram to illustrate different operating states of the gear arrangement according to Figure 1.

[0025] A gear assembly designated by reference numeral 1, for example, can be used as an actuator in robotics and comprises a wave gear 2, which, depending on the operating state, either functions as a reduction gear or runs freely. Depending on the operating mode, a switchable clutch 3 of the gear assembly 1 is open or closed. When the clutch 3 is open, an input shaft 6 of the gear assembly 1 is rotationally fixed to an output shaft 7. In this case, a clutch actuation mechanism 5, which is designed both to actuate the clutch 3 and is itself a clutch, namely an overload clutch, is closed. The detent clutch actuation mechanism 5 comprises an input torque transmission structure 16, which is located on a cover plate 4 that is fixedly connected to the input shaft 6.An associated output-side torque transmission structure 17 is located on a clutch disc 15, which in the exemplary embodiment is designed to interact with a clutch lining 14 belonging to the clutch 3. When the clutch actuation mechanism 5 opens or closes, the output shaft 7, together with the clutch disc 15, is displaced axially along the output shaft 7 and thus along the entire transmission assembly 1. Displacement of the input-side shaft 6 is not provided for.

[0026] If a torque is introduced into shaft 6 on the input side of the transmission assembly 1, this torque is transmitted to the output shaft 7 as long as no excessive braking torque acts on the output shaft 7. If the corresponding torque limit is exceeded, the ramp contours defined by the torque transmission structures 16, 17 open the clutch actuation mechanism 5 while simultaneously closing the clutch 3, which is designed as a friction clutch. At this moment, the wave gear 2 engages.

[0027] A housing designated 8 for the wave gear 2 can simultaneously serve as the housing for the entire gear assembly 1. The wave gear 2 comprises a rolling bearing 19, which is part of a wave generator designated 18. An inner ring 20 of the rolling bearing 19, located on the shaft 6, has an elliptical shape, deviating from a circular form. Balls, acting as rolling elements 21, roll on the inner ring 20 and are guided in a cage 22. An outer ring 23 of the rolling bearing 19 of the wave generator 18 continuously adapts to the non-circular shape of the inner ring 20 as the shaft 6 rotates. The outer ring 23 is surrounded, without a fixed connection, by an elastic, externally toothed gear element 24. The gear element 24 has a toothed section 25 and a collar 26, which is attached to the housing 8. Overall, the elastic gear element 24 thus represents a collar sleeve.The toothing of the elastic gear element 24, located at section 25, engages partially, namely exclusively at two diametrically opposed points, with the internal teeth of a gear component 28. The number of teeth of the external teeth of the elastic gear element 24 differs slightly, by two, from the number of teeth of the internal teeth of the gear component 28, with the gear element 24 having two fewer teeth than the gear component 28. This results in a full rotation of the shaft 6, i.e., a 360-degree rotation, being converted into only a slight pivoting of the gear component 28.

[0028] The gearing component 28 is part of an output element of the wave gear 2, designated as 10. A cylindrical section 12 of the rigid output element 10 connects to the gearing component 28. In the exemplary embodiment, a rolling bearing 9, designed as a double-row angular contact needle bearing, is provided for supporting the output element 10 in the housing 8. A seal 11, designed as a contact seal, seals the rolling bearing 9. Static seals within the housing 8 are designated by 27.

[0029] A ring-shaped section 13, which is also part of the output element 10, is connected to the cylindrical section 12 on the side facing away from the gearing component 28. The clutch lining 14 is located on the ring-shaped section 13 in this case.

[0030] Regarding the automatic switching function of the gear arrangement 1 between two different operating modes, reference is made to the idealized diagram in Figure 2. This diagram illustrates the curves of various torques M and rotational speeds n as a function of time t. It is assumed that the gear arrangement 1 is initially operated in direct drive mode, i.e., with the wave gear 2 deactivated. In this mode, the torque M increases until a switching torque Mu is reached, which occurs at a switching point tu. At the switching point tu, i.e., when the switching torque Mu, which represents a torque limit, is exceeded, the clutch 3 is closed by the clutch actuation mechanism 5, which is accompanied by the release of the torsionally rigid coupling between the input shaft 6 and the output shaft 7.As already explained with reference to Figure 1, this activates the wave gear 2, thereby reducing the output torque of the gear arrangement 1 to the value M. a increases. This occurs while an input-side rotational speed n e The rotational speed of shaft 6 remains at least approximately constant. Simultaneously, the rotational speed of output shaft 7, denoted by nA, decreases. The input-side rotational speed, denoted by M e The specified torque can either remain approximately at the level of the switching torque Mu, as sketched in Figure 2, or drop to a lower level. Since the clutch actuation mechanism 5 does not fully open, the input and output torque levels M can vary. e , MA, as shown in Figure 2, exhibit fluctuations resulting from the shape of the torque transmission structures 16, 17. The magnitude of the different speed and torque levels n e , nA, M e , MA is not shown to scale in Figure 2.

[0031] List of reference signs

[0032] 1 Gear arrangement

[0033] Wave gear

[0034] coupling

[0035] End plate

[0036] clutch actuation mechanism

[0037] Wave

[0038] Output wave

[0039] Housing

[0040] rolling bearings

[0041] 10 Output element of the wave gear

[0042] 11 Seal

[0043] 12 cylindrical section

[0044] 13 ring-shaped section

[0045] 14 Clutch lining

[0046] 15 Clutch disc

[0047] 16 Torque transmission structure, input side

[0048] 17 Torque transmission structure, output side

[0049] 18 wave generator

[0050] 19 rolling bearings of the shaft generator

[0051] 20 inner ring

[0052] 21 rolling elements, ball

[0053] 22 cage

[0054] 23 Outer ring

[0055] 24 elastic gear element

[0056] 25 toothed section

[0057] 26 collars

[0058] 27 static seal

[0059] 28 Gear component

[0060] M torque

[0061] MA torque, output shaft; Me torque, input side

[0062] Mu switching torque, torque limit n speed nA speed, output shaft n e Speed, input side t Time tu Switching time

Claims

Patent claims 1. Gear arrangement (1) comprising a wave gear (2), a clutch (3) located on the output side of the wave gear (2) including a clutch actuation mechanism (5), and an output shaft (7), wherein an input shaft (6) of a wave generator (18) of the wave gear (2) is rotationally fixed to the output shaft (7) via the closed clutch actuation mechanism (5) when the clutch (3) is open, as long as a braking torque acting on the output shaft (7) does not exceed a torque limit, whereas if the torque limit is exceeded, the clutch (3) is held closed by means of the clutch actuation mechanism (5), which at the same time releases the rotationally fixed coupling between the input shaft (6) and the output shaft (7), thereby establishing a power flow between the input shaft (6) and the output shaft (7) via the wave gear (2).

2. Gear arrangement (1 ) according to claim 1 , characterized in that the wave gear (2) has an elastic collar-shaped, externally toothed gear element (24) which is held on a housing (8).

3. Gear arrangement (1 ) according to claim 2, characterized in that a toothed section (25) of the elastic gear element (24) meshes with a toothed component (28) which is firmly connected to an element (15) of the coupling (3).

4. Gear arrangement (1 ) according to claim 3, characterized in that the gearing component (28) is mounted in the housing (8) in a rolling bearing.

5. Gear arrangement (1 ) according to claim 4, characterized in that a multi-row angular contact needle bearing (9) is provided for supporting the gearing component (28).

6. Gear arrangement (1 ) according to one of claims 1 to 5, characterized in that the shaft generator (18) comprises a rolling bearing (19), in particular a ball bearing.

7. Gear arrangement (1 ) according to one of claims 1 to 6, characterized in that the clutch actuation mechanism (5) is designed as a latching overload clutch.

8. Method for operating a gear arrangement (1) designed according to claim 1, wherein in a first operating phase a rotation of an input shaft (6) is directly transferred to an output shaft (7) and in a second operating phase, in which a higher braking torque acts on the output shaft (7) compared to the first operating phase, the rotation of the input shaft is converted into a rotation of the output shaft (7) via a wave gear (2) provided as a reduction gear.

9. Method according to claim 8, characterized in that the switching between the different operating phases takes place automatically depending on the torque braking the output shaft (7).

10. Method according to claim 9, characterized in that the switching is forced by a clutch actuation mechanism (5) which in the first operating phase couples the input shaft (6) to the output shaft (7) in a rotationally fixed manner.

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