DE102024111183A1 - Gear arrangement and method for operating a gear arrangement - Google Patents

Abstract

A gear arrangement which can be used in particular in an actuator comprises a harmonic drive (2), a clutch (3) located on the output side of the harmonic drive (2), including a clutch actuation mechanism (5), and an output shaft (7), wherein an input-side shaft (6) of a wave generator (18) of the harmonic drive (2) is coupled in a rotationally fixed manner to the output shaft (7) via the closed clutch actuation mechanism (5) when the clutch (3) is simultaneously open, as long as a braking torque acting on the output shaft (7) does not exceed a torque limit value. However, when the torque limit value is exceeded, the clutch (3) is kept closed by means of the clutch actuation mechanism (5), which at the same time cancels the rotationally fixed coupling between the input-side shaft (6) and the output shaft (7), thus establishing a power flow between the input-side shaft (6) and the output shaft (7) via the harmonic drive (2).

Description

The invention relates to a gear assembly comprising a harmonic drive. Furthermore, the invention relates to a method for operating such a gear assembly.

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, an output shaft of a wave gear can rotate either in the same direction or in the opposite direction to an input shaft.

From the 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 the rolling bearing, with a cage of the rolling bearing also being designed as a locking element acting in the axial direction.

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

One in the DE 10 2016 222 897 A1 The described strain wave gear provides for torque transmission via an Oldham coupling. An Oldham coupling is a compensating coupling, not a switchable coupling.

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

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

The DE 10 2021 119 597 A1 The subject is 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.

• „ Präzisionswellgetriebe Baureihe RT“, Schaeffler Technologies AG & Co. KG, Schweinfurt, TPI 275 / de-DE / DE / 2022-10

Further information on shaft gears can be found in the following publication:

• " Precision strain wave gears, RT series“, Schaeffler Technologies AG & Co. KG, Schweinfurt, TPI 275 / de-DE / DE / 2022-10

The invention is based on the object of further developing transmission technology which is based on wave gears and 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.

This object is achieved according to the invention by a gear arrangement having the features of claim 1. The object is also achieved by a method for operating a gear 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 gear arrangement, and vice versa.

The gear arrangement according to the application comprises a strain wave gear, a clutch located on the output side of the strain wave gear, including a clutch actuation mechanism, and an output shaft. An input shaft of a strain wave generator of the strain wave gear is non-rotatably coupled to the output shaft via the closed clutch actuation mechanism while the clutch is simultaneously open, as long as a braking torque acting on the output shaft does not exceed a torque limit. However, if the torque limit is exceeded, the clutch is held closed by the clutch actuation mechanism, which simultaneously releases the non-rotatable coupling between the input shaft and the output shaft, thus establishing a power flow between the input shaft and the output shaft via the strain wave gear. At the same time, if a speed difference exists, power can still be fed directly from the input shaft to the output shaft to a lesser extent.

The clutch actuation mechanism thus has multiple functions: Firstly, it can establish and release a rotationally fixed connection between the input and output shafts. Secondly, the clutch actuation mechanism actuates the clutch on the output side of the strain wave gear, which selectively activates or deactivates the strain wave gear.

The strain wave gear of the gear assembly 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 an inherently rigid toothed component, which is firmly connected to an element of the coupling of the gear assembly. The coupling is the device designed to establish a torsionally rigid connection between the output-side element of the strain wave gear and the output shaft of the entire gear assembly.

The aforementioned gearing component can be assigned to the output-side element of the strain wave gear. This element is mounted in the housing of the gear assembly, for example, on a roller bearing. A double-row needle, roller, or ball bearing is particularly suitable as a roller bearing, which is designed to absorb radial loads, axial loads, and tilting loads.

The wave generator can generally 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, a ball bearing. In either case, an inner ring of the bearing is inherently rigid, whereas an outer ring of the rolling bearing is flexible. Embodiments in which a bearing ring is formed directly by a section of the flexible transmission element are also possible.

In principle, the gear arrangement can include a wide variety of bearing types. In addition to rolling and plain bearings, for example, in the form of hydrodynamic bearings, magnetic bearings are also conceivable.

As far as the clutch actuation mechanism is concerned, the designs of latching overload clutches can be used in principle. In this context, the DE 10 2019 120 320 A1 This concerns a safety coupling for a robot joint. A characteristic of such couplings is that opening the coupling in the event of an overload is accompanied by a radial displacement between two elements belonging to the coupling.

The method for operating the gear arrangement according to the application is generally characterized in that, in a first operating phase, a rotation of an input-side shaft is transmitted directly 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-side shaft is converted into a rotation of the output shaft via a wave gear provided as a reduction gear.

Switching between the different operating phases can occur automatically depending on the torque braking the output shaft. In particular, switching can be enforced by a clutch actuation mechanism that, during the first operating phase, torque-locks the input shaft to the output shaft.

The input shaft of the gear assembly, like the output shaft, can be a solid or hollow shaft. Optionally, the gear assembly is equipped with a torque sensor.

• 1 eine Getriebeanordnung einschließlich eines automatisch als Untersetzungsgetriebe zuschaltbaren Wellgetriebes in einer Schnittdarstellung,
• 2 ein Diagramm zur Erläuterung verschiedener Betriebszustände der Getriebeanordnung nach 1.

An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. The drawings show, partially schematically:

• 1 a gear arrangement including a wave gear that can be automatically switched on as a reduction gear in a sectional view,
• 2 a diagram to explain different operating states of the gear arrangement according to 1 .

A gear assembly, designated overall by reference numeral 1, can be used, for example, as a servo gear in robotics and comprises a harmonic drive 2, which, depending on the operating state, either functions as a reduction gear or runs idle. 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-side shaft 6 of the gear assembly 1 is connected in a rotationally fixed manner to an output shaft 7. A clutch actuation mechanism 5, which is provided for actuating the clutch 3 and also constitutes a clutch itself, namely an overload clutch, is closed.

The detent-operating clutch actuation mechanism 5 comprises an input-side torque transmission structure 16, which is located on a cover plate 4, which is firmly connected to the input-side shaft 6. An associated output-side torque transmission structure 17 is located on a clutch disc 15, which in the exemplary embodiment is provided for interaction with a clutch lining 14, which is assigned to the clutch 3. When opening or closing the clutch actuation mechanism 5, the output shaft 7 together with the clutch disc 15 is moved in the axial direction of the output shaft 7 and thus of the entire transmission arrangement 1. A shift of the input-side shaft 6 is not intended.

If a torque is introduced into shaft 6 on the input side of the gear assembly 1, this torque is transmitted to the output shaft 7, as long as the output shaft 7 is not subjected to excessive braking torque. 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 strain wave gear 2 comes into operation.

A housing, designated 8, of the wave gear 2 can also be designed as the housing of the entire gear assembly 1. The wave gear 2 comprises a rolling bearing 19, which is assigned to a wave generator, designated 18 overall. An inner ring 20 of the rolling bearing 19, located on the shaft 6, has an elliptical shape that deviates from a circular shape. Balls roll on the inner ring 20 as rolling elements 21, which are guided in a cage 22. An outer ring 23 of the rolling bearing 19 of the wave generator 18 permanently adapts to the non-circular shape of the inner ring 20 as the shaft 6 rotates. The outer ring 23 is surrounded, without any 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 fastened to the housing 8. Overall, the elastic gear element 24 thus represents a collar sleeve.

The toothing of the elastic gear element 24 located on section 25 engages partially, namely exclusively at two diametrically opposite points, with the internal toothing of a toothed component 28. The number of teeth of the external toothing of the elastic gear element 24 differs slightly, namely by two, from the number of teeth of the internal toothing of the toothed component 28, with the gear element 24 having two fewer teeth than the toothed component 28. This results in a full revolution of the shaft 6, i.e., a rotation of 360 degrees, being converted into only a slight pivoting of the toothed component 28.

The toothed component 28 is assigned to an output element of the strain wave gear 2, designated overall by 10. A cylindrical section 12 of the inherently rigid output element 10 adjoins the toothed component 28. To support the output element 10 in the housing 8, a rolling bearing 9 is provided in the exemplary embodiment. This bearing is designed as a double-row angular contact needle bearing. A seal 11, designed as a contact seal, seals the rolling bearing 9. Static seals within the housing 8 are designated by 27.

Connected to the cylindrical portion 12 on the side facing away from the toothed component 28 is an annular disc-shaped portion 13, which is also assigned to the output element 10. In this case, the clutch lining 14 is located on the annular disc-shaped portion 13.

Regarding the automatic switching function of the gear arrangement 1 between two different operating modes, reference is made to the idealized diagram according to 2 This diagram illustrates the curves of various torques M and speeds n as a function of time t. It is assumed that the gear assembly 1 is initially operated in direct drive mode, i.e., with the strain wave gear 2 deactivated. In this case, the torque M increases up to a switching torque Mu, which occurs at a switching time tu.

At the switching point tu, i.e. when the switching torque Mu representing a torque limit is exceeded, the clutch 3 is closed by the clutch actuation mechanism 5, which is accompanied by a removal of the torsionally rigid coupling between the input-side shaft 6 and the output shaft 7. As already shown in 1 explained, the wave gear 2 is activated, whereby the output torque of the gear arrangement 1 increases to the value M _a . This occurs while the input speed n _e of the shaft 6 remains at least approximately constant. The speed of the output shaft 7, designated n _A, decreases simultaneously. The input torque, designated M _e, can either, as in 2 outlined, remain approximately at the level of the switching torque Mu or drop to a lower level. Since the clutch actuation mechanism 5 does not open completely, the input and output side levels of the torques M _e , M _A , as in 2 shown, fluctuations, resulting from the shape of the torque transmission structures 16, 17. The height of the different speed and torque levels n _e , n _A , M _e , M _A is in 2 not shown to scale.

List of reference symbols

1

Gear arrangement

2

Wave gear

3

coupling

4

End plate

5

Clutch actuation mechanism

6

Wave

7

Output shaft

8

Housing

9

Rolling bearings

10

Output element of the strain wave gear

11

seal

12

cylindrical section

13

annular disc-shaped section

14

clutch lining

15

clutch disc

16

Torque transmission structure, input side

17

Torque transmission structure, output side

18

Wave generator

19

Rolling bearings of the wave generator

20

inner ring

21

Rolling element, ball

22

cage

23

Outer ring

24

elastic gear element

25

toothed section

26

collar

27

static seal

28

Gearing component

M

torque

MA

Torque, output shaft

Me

Torque, input side

Mu

Switching torque, torque limit

n

speed

n/a

Speed, output shaft

no

Speed, input side

t

Time

you

Switchover time

QUOTES CONTAINED IN THE DESCRIPTION

This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10 2017 110 678 B3 [0003]
• DE 10 2019 102 264 A1 [0004]
• DE 10 2016 222 897 A1 [0005]
• DE 10 2015 224 897 A1 [0006]
• EP 0 514 829 B1 [0007]
• EP 0 741 256 B1 [0007]
• DE 10 2021 119 597 A1 [0008]
• DE 10 2019 120 320 A1 [0018]

Cited non-patent literature

• Precision wave gear units, RT series“, Schaeffler Technologies AG & Co. KG, Schweinfurt, TPI 275 / de-DE / DE / 2022-10 [0009]

Claims (10)

Gear arrangement (1) comprising a harmonic drive (2), a clutch (3) located on the output side of the harmonic drive (2), including a clutch actuation mechanism (5), and an output shaft (7), wherein an input-side shaft (6) of a wave generator (18) of the harmonic drive (2) is coupled in a rotationally fixed manner to the output shaft (7) via the closed clutch actuation mechanism (5) when the clutch (3) is simultaneously open, as long as a braking torque acting on the output shaft (7) does not exceed a torque limit value, whereas when the torque limit value is exceeded, the clutch (3) is kept closed by means of the clutch actuation mechanism (5), which at the same time cancels the rotationally fixed coupling between the input-side shaft (6) and the output shaft (7), whereby a power flow is established between the input-side shaft (6) and the output shaft (7) via the harmonic drive (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). Gear arrangement (1) according to Claim 2 , characterized in that a toothed portion (25) of the elastic transmission element (24) meshes with a toothed component (28) which is fixedly connected to an element (15) of the coupling (3). Gear arrangement (1) according to Claim 3 , characterized in that the toothed component (28) is mounted on roller bearings in the housing (8). Gear arrangement (1) according to Claim 4 , characterized in that a multi-row angular contact needle bearing (9) is provided for supporting the toothed component (28). Gear arrangement (1) according to one of the Claims 1 until 5 , characterized in that the wave generator (18) comprises a rolling bearing (19), in particular a ball bearing. Gear arrangement (1) according to one of the Claims 1 until 6 , characterized in that the clutch actuating mechanism (5) is designed as a locking overload clutch. Procedure for operating a Claim 1 formed gear arrangement (1), wherein in a first operating phase a rotation of an input-side shaft (6) is transmitted directly 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-side shaft is converted into a rotation of the output shaft (7) via a wave gear (2) provided as a reduction gear. Procedure according to Claim 8 , characterized in that the switching between the different operating phases takes place automatically as a function of the torque braking the output shaft (7). Procedure according to Claim 9 , characterized in that the switching is enforced by a clutch actuating mechanism (5) which, in the first operating phase, couples the input-side shaft (6) to the output shaft (7) in a rotationally fixed manner.