Reduction gear, drive assembly, and method for operating such a drive assembly

Abstract

The invention relates to a reduction gear (10, 20) comprising a first reduction stage (11, 21), a second reduction stage (12, 22) and a third reduction stage (13, 23). The first reduction stage (11, 21) is designed as a first planetary gear set (110), having a drivable first sun gear (111), having a first spider (112) and having a first ring gear (113), wherein first planetary gears (114), which each engage into the first sun gear (111) and into the first ring gear (113), are mounted on the first spider (112). The second reduction stage (12) is designed as a second planetary gear set (120), having a second sun gear (121), having a second spider (122) and having a second ring gear (123). Second planetary gears (124), which each engage into the second sun gear (121) and into the second ring gear (123), are mounted on the second spider (122). The second sun gear (121) is connected to the first spider (112) in a rotationally fixed manner. The third reduction stage (13) has a pinion (131, 231) which is connected to the second spider (122) in a rotationally fixed manner. The pinion (131, 231) engages into a third ring gear (31, 41). The invention further proposes a drive assembly (1) comprising two such reduction gears (10, 20). Finally, a method for operating such a drive assembly (1) is specified.

Description

[0001] ZF Friedrichshafen AG File 306580-WO-PCT Friedrichshafen 2025-12-05 Reduction gear, drive arrangement and method for operating such a drive arrangement

[0002] The present invention relates to a reduction gear, a drive arrangement for a robot arm with two such reduction gears, and a method for driving such a drive arrangement.

[0003] Planetary gearboxes offer the advantage over other gearbox types of enabling large gear ratios or reductions in a compact design. Furthermore, planetary gearboxes can transmit high torques while achieving high angular accuracy. Therefore, planetary gearboxes are particularly suitable for use in drive systems for pivoting robot arms.

[0004] From DE 102006046581 A1, a reduction gear with three reduction stages is known, in which a first reduction stage is designed as a planetary gear, with a driven first sun gear, with several first planet gears rotatably mounted in a first rotatably mounted planet carrier, which are in simultaneous meshing with the first sun gear and a likewise rotatably mounted first ring gear. In one embodiment of DE 102006046581 A1, this so-called first reduction stage is further preceded by another reduction stage designed as a planetary stage.

[0005] The reduction gear further comprises a second reduction stage downstream of the first, with two pinions that mesh with a large gear at different points on its circumference. The first pinion is rotationally fixed to the first planet carrier, and the second pinion is driven by a reversing gear stage connected to the first ring gear. The large gear acts as a stator, and the output is formed by an assembly in which the pinions are also mounted, so that during operation the two pinions rotate around the central axis of the large gear like planetary gears.

[0006] Furthermore, a control device for a ship's propulsion system with an electric steering motor and a steering gearbox is known from DE 102008042599 A1. A steering gearbox described therein (ZF Friedrichshafen AG file 306580-WO-PCT Friedrichshafen 2025-12-05) consists of two concentrically arranged planetary gear sets, which form a first and a second reduction stage. A spur gear stage downstream of the planetary gear sets of the steering gearbox forms a third reduction stage.

[0007] The object of the present invention is to provide a reduction gear which, with the simplest possible design, can transmit the highest possible reduction ratio and high torque. Furthermore, a method for driving a robot arm using such a reduction gear is to be provided.

[0008] These tasks are solved by a reduction gear according to claim 1, by a drive arrangement according to claim 7 and by a method according to claim 12. Advantageous embodiments and further developments result from the respective dependent claims and from the description.

[0009] A reduction gear is proposed comprising a first reduction stage, a second reduction stage, and a third reduction stage. The first reduction stage is designed as a first planetary gear set, with a driven first sun gear, a first carrier, and a first ring gear, wherein the first planet gears are mounted on the first carrier and mesh with the first sun gear and the first ring gear, respectively.

[0010] The second reduction stage is designed as a second planetary gear set, comprising a second sun gear, a second carrier, and a second ring gear. The second carrier supports two planet gears, each engaging with the second sun gear and the second ring gear. The first and second ring gears can be formed as a single ring gear component. In this case, the teeth of the first and second planet gears can engage with each other at two axially separate points within the ring gear component. Alternatively, the ring gear component can have a single ring gear with teeth into which the teeth of the first and second planet gears engage. Such a ring gear extends axially across both the first and second planetary gear sets.In a preferred ZF Friedrichshafen AG file 306580-WO-PCT Friedrichshafen 2025-12-05 embodiment, the first ring gear and the second ring gear have an identical number of teeth and an identical gear module, so that the two axially separated gears can be manufactured in one clamping operation.

[0011] The second sun gear is connected to the first hub in a twisted manner, so that the second sun gear is driven via the first hub during operation. The third reduction stage has a pinion that is connected to the second hub in a twisted manner, so that the pinion of the third reduction stage is driven by the second hub during operation. The pinion engages with a third ring gear. The third ring gear, or rather its teeth, can have a higher number of teeth compared to the pinion in order to achieve a high gear ratio even in the third reduction stage.

[0012] An advantage of the present invention is that, compared to the externally toothed large gear known from the prior art, the number of teeth of an internally toothed ring gear in the third reduction stage, with the same gear module and the same center distance of a drive shaft of the first reduction stage to a central axis of rotation, is necessarily greater than the number of teeth of the externally toothed large gear. This results in a higher gear ratio.

[0013] Another advantage concerns the stress on the gear teeth in the third gear stage when transmitting high torques, particularly the resulting flank pressure. The flank pressure is lower in the proposed gear pairing of the third gear stage, consisting of the pinion and the third ring gear, because the torque is transmitted via a convex-concave flank pairing. Compared to the prior art concave-concave flank pairing of a pinion engaging an externally toothed large gear, the flank pressure in the convex-concave flank pairing according to the invention is considerably lower. A further advantage arises from the fact that the gear efficiency of an external-internal gear pairing is higher than that of an external-external gear pairing.

[0014] A twisted connection is understood to be a connection which, according to ZF Friedrichshafen AG file 306580-WO-PCT Friedrichshafen 2025-12-05, can be implemented as a positive-locking, friction-locking, or material-locking connection, for example, by means of a suitable splined connection, screw connection, shrink-fit connection, or welding. The definition also includes a one-piece construction of the twistedly connected components. Furthermore, the definition also includes the kinematic interposition of a constant gear ratio between the two twistedly connected components, such that a first component—when driven—rotates continuously at a speed that differs from the speed of the second component by a predefined factor of this gear ratio.

[0015] In one embodiment, the third transmission stage comprises exactly one pinion that engages with the third ring gear. This means that this embodiment is significantly simpler in design and requires fewer parts compared to the prior art mentioned above, because the third transmission stage has only a single pinion that engages with an internal toothing of the third ring gear. A second pinion, as known in the prior art mentioned above, is therefore unnecessary.

[0016] According to a first alternative of the invention, the third ring gear can be attached to a stationary base frame or formed integrally with such a stationary base frame. The stationary base frame can be designed as a robot foot that supports a robot arm rotatably mounted on it. The reduction gear according to the invention can be part of a drive arrangement with which the robot arm, which is pivotably arranged on the robot foot, can be moved. In this embodiment, the first and second reduction gears are mounted in a pivot housing that is rotatable relative to the stationary base frame and are at least partially arranged in the pivot housing. The first ring gear and the second ring gear can be rigidly arranged in the pivot housing or formed integrally with the pivot housing.In this embodiment, the swivel housing can be described as the output element of the reduction gear, since it rotates about a central axis of rotation as a result of the pinion being supported in the third ring gear, which is stationary on the base frame. ZF Friedrichshafen AG File 306580-WO-PCT Friedrichshafen 2025-12-05. Alternatively, according to a second embodiment of the invention, the first and second ring gears can be attached to a stationary base frame or formed integrally with a stationary base frame, whereas the third ring gear is arranged on a swivel housing that is rotatable relative to the base frame or formed integrally with the rotatable swivel housing. In this alternative embodiment, the stationary base frame can be designed as a robot foot that supports a robot arm rotatably mounted on it.This embodiment has the advantage of exhibiting a tighter tolerance chain for the components compared to the embodiment described above. The first and second planetary gear sets, as well as a drive motor connected to the first sun gear, can be mounted on the stationary base frame. Therefore, fewer masses need to be accelerated and moved when the robot arm is rotated or pivoted.

[0017] According to one embodiment, the pinion and the third ring gear are each conically designed, with adjustment means for setting the axial position of the pinion relative to the third ring gear. Accordingly, the teeth of the pinion and the third ring gear can be designed as beveloid teeth. By axially displacing the conical pinion and the conical third ring gear relative to each other, the backlash can be minimized. This is particularly advantageous in a reduction gearbox as part of a drive for a robot arm, because it allows desired target positions to be approached and maintained with high accuracy when pivoting the robot arm. Adjustment shims can serve as the adjustment means; these shims, with a selectable thickness, can be arranged on a bearing of the pinion or an associated pinion shaft in such a way that a desired axial position of the pinion is set.In this way, the backlash between the pinion and the third ring gear can be adjusted or eliminated, thus achieving the precision necessary for a robot gearbox. As an alternative to this embodiment with a conical pinion and third ring gear, the teeth of the pinion and the third ring gear can also be designed with standard and at least substantially cylindrical involute teeth. Two electric motors can be used as drives for the precise control of desired pivoting positions of the robot arm, operated according to a method described below (ZF Friedrichshafen AG File 306580-WO-PCT Friedrichshafen 2025-12-05). Thus, the entire drive assembly can be manufactured simply and cost-effectively with standard gear teeth.

[0018] In an alternative design, all gear teeth of the three reduction stages can be standard involute gears without tapered gears. This simplifies the manufacturing and assembly of the reduction gear. Using a method described below for a drive arrangement with two reduction gears, backlash can still be eliminated and a target position can be approached with high precision.

[0019] For the most twisted connection between the pinion of the third reduction stage and the second web, the pinion's running teeth can be designed to engage with internal teeth on the second web. In this design, at least a significant portion of the torque is transmitted via the extended running teeth of the pinion, which engage with the internal teeth of the second web. To minimize backlash in the reduction gear, this connection incorporates a tight fit.

[0020] Alternatively or additionally to the twisted connection described above, the pinion of the third reduction stage can be centered in the second web by means of a pinion shaft that is centered in a bore of the second web by means of an interference fit. An interference fit is also called an interference fit. This prevents the pinion from tilting relative to the second web. The pinion shaft can be manufactured in one piece with the pinion, or the pinion can be manufactured separately from the pinion shaft and then twisted onto the pinion shaft. The pinion, together with the pinion shaft, can be attached to the second web by means of a screw, so that the pinion is axially fixed and secured to the second web by said screw.

[0021] Another aspect of the invention relates to a drive arrangement for a robot arm. Such a drive arrangement comprises a first and a second electric motor as well as a first and a second reduction gear, each configured according to one of the embodiments described above. In this case, the first electric motor is effectively connected to the sun gear of the first planetary gear set of the first reduction gear, and the second electric motor is effectively connected to the sun gear of the first planetary gear set of the second reduction gear. In other words, each electric motor drives one of the two reduction gears. However, both reduction gears drive a common ring gear, namely the third ring gear described above.Accordingly, the third ring gear of the first and second reduction gears is designed as a common third ring gear into which the pinions of the first and second reduction gears engage. In this way, sufficient drive power can be achieved to pivot the robot arm at the required speed.

[0022] In a first embodiment of the drive arrangement, the first and second reduction gears are at least partially housed in a common swivel housing that is rotatable relative to the third ring gear, with the third ring gear being attached to a stationary base frame of the robot. In this embodiment, the swivel housing can thus be rotated about a central axis of rotation relative to the stationary base frame. This formulation also includes the possibility that the third ring gear is manufactured integrally with the stationary base frame. The swivel housing can also be called a carousel. The robot arm can be rigidly attached to the swivel housing, so that the robot arm is rotated or pivoted in a desired direction by rotating the swivel housing.In this embodiment, the first ring gear and the second ring gear can each be rigidly arranged in the swivel housing or formed integrally with the swivel housing.

[0023] According to a preferred embodiment of the first embodiment of the drive arrangement described above, an outer circumferential surface of the third ring gear is designed as a sealing surface, and a sealing ring is arranged on the sealing surface to seal an interior space of the swivel housing against an intermediate space. This intermediate space adjoins a rolling bearing by which the swivel housing is rotatably mounted in the stationary base frame. The aforementioned rolling bearing can, for example, be designed as a crossed roller bearing. ZF Friedrichshafen AG File 306580-WO-PCT Friedrichshafen 2025-12-05

[0024] In an alternative second embodiment of the drive arrangement, the first and second electric motors, as well as the first and second reduction gears, are mounted on the robot's stationary base frame, while the third ring gear is mounted on the swivel housing, which is rotatable relative to the base frame, or is integrally formed with the swivel housing. In this second embodiment, the connection between the base frame and the swivel housing is reversed compared to the first embodiment. The components of the two reduction gears are no longer mounted in the swivel housing in the second embodiment, but rather in the stationary base frame. The output element in the second embodiment of the drive arrangement is the third ring gear, which rotates around a central axis of rotation together with the swivel gearbox.

[0025] Finally, another aspect of the invention relates to a method for operating a drive arrangement as described above. The proposed method comprises the following steps:

[0026] - Motorized driving of the first and second electric motors to swivel the robot arm towards a target position,

[0027] - Switching the second electric motor to generator mode before the target position is reached, so that a braking torque is generated that opposes the drive torque of the first electric motor,

[0028] - Moving the robot arm to its target position by the drive torque of the first electric motor against the braking torque of the second electric motor.

[0029] CONTENT OF THE DRAWINGS

[0030] The present invention is explained in more detail below with reference to the accompanying figures of the specified embodiments. These figures show:

[0031] Figure 1 is a schematic representation of a first embodiment of a drive arrangement according to the invention; ZF Friedrichshafen AG File 306580-WO-PCT Friedrichshafen 2025-12-05 Figure 2 is a sectional drawing of the first embodiment of the drive arrangement according to the invention;

[0032] Figure 3 shows an enlarged section from Fig. 2 and

[0033] Figure 4 shows a schematic representation of a second embodiment of a drive arrangement according to the invention;

[0034] Figure 5 shows a schematic representation of the steps of a method according to the invention.

[0035] The accompanying drawings are intended to provide a further understanding of the embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain the principles and concepts of the invention. The elements of the drawings are not necessarily shown to scale.

[0036] DESCRIPTION OF EXAMPLES OF EXECUTION

[0037] The first embodiment of a drive arrangement 1 for a robot arm of a robot, shown in Fig. 1, comprises a first electric motor 100 and a second electric motor 200, as well as a first reduction gear 10 and a second reduction gear 20. The first reduction gear 10 is driven by the first electric motor 100 and the second reduction gear 20 is driven by the second electric motor 200.

[0038] Each of the two reduction gears 10, 20 comprises a first reduction stage 11, 21, a second reduction stage 12, 22, and a third reduction stage 13, 23, wherein the drive power transmitted via the two reduction gears 10, 20 is summed in the third reduction stage 13, 23 onto a common third ring gear 31. In other words, the drive power of the two electric motors 100, 200 is combined at the third ring gear 31. In the section view shown in Fig. 2, only the first reduction gear 10 and the connection point 104 for the first electric motor 100 are visible. The entire ZF Friedrichshafen AG file 306580-WO-PCT Friedrichshafen 2025-12-05 drive arrangement 1 also includes the second reduction gear 20 and the second electric motor 200, which are arranged in the circumferential direction of the third ring gear 31 offset to the first reduction gear 10 and the first electric motor 100.The two reduction gears 10 and 20 are of the same design. Therefore, only one of the two essentially identical reduction gears 10 and 20, namely the first reduction gear 10 with its associated first electric motor 100, will be described in more detail below with reference to Fig. 1 and Fig. 2.

[0039] The first reduction stage 11 is designed as a first planetary gear set 110. The first planetary gear set 110 comprises a first sun gear 111 driven by the first electric motor 100, a first carrier 112, and a first ring gear 113. First planet gears 114 are mounted on the first carrier 112, each engaging with the first sun gear 111 and the first ring gear 113, respectively.

[0040] The second reduction stage 12 is designed as a second planetary gear set 120 and comprises a second sun gear 121, a second carrier 122, and a second ring gear 123, wherein second planet gears 124 are mounted on the second carrier 122, each engaging with the second sun gear 121 and the second ring gear 123. The second sun gear 121 is twist-resistant and preferably rigidly connected to the first carrier 112.

[0041] The third reduction stage 13 has a pinion 131, which is twisted and connected to the second web 122. The pinion 131 meshes with an internal toothing of a third ring gear 31. The third ring gear 31 is rigidly attached to a stationary base frame 30. The third ring gear 31 can, for example, be screwed to the stationary base frame 30.

[0042] In the drive arrangement 1, the pinion 131 of the first reduction gear 10 engages at a first point on the inner circumference of the third ring gear 31 with its internal teeth. At a second point on the inner circumference of the third ring gear 31, the pinion 231 of the second reduction gear 20, which is driven by the second electric motor 200 via the second reduction gear 20, engages with its internal teeth. ZF Friedrichshafen AG File 306580-WO-PCT Friedrichshafen 2025-12-05. The first electric motor 100, the second electric motor 200, the first reduction gear 10, and the second reduction gear 20 are each mounted on a common pivot housing 40 that is rotatable relative to the third ring gear 31. In Figures 2 and 3, only the connection point 104 for the first electric motor 100 is shown.

[0043] The swivel housing 40 can be rotated about a central axis of rotation 44 relative to the stationary base frame 30. The first electric motor 100 and the second electric motor 200 each have a motor housing, which is attached to the swivel housing 40. The first electric motor 100 and the second electric motor 200 also each have a stator 102, 202 and a rotor 103, 203. The respective stator 102, 202 is mounted in the motor housing of the associated electric motor 100 or 200 and is thus also fixed in position relative to the swivel housing 40. The rotors 103 and 203 are rotatably mounted in their respective motor housings.

[0044] The first ring gear 113 and the second ring gear 123 are each rigidly arranged in the pivot housing 40. The first ring gear 113 and the second ring gear 123 are formed on a common ring gear component 126. The first planet gears 114 and the second planet gears 124 engage with their teeth in two axially separate areas of the ring gear component 126, i.e., in the respective first ring gear 113 and the second ring gear 123.

[0045] In the enlarged section of Fig. 3, it can be seen that in the first embodiment, an outer circumferential surface of the third ring gear 31 is designed as a sealing surface 138, on which a seal 139 is arranged. The seal 139 seals an interior space 45 of the pivot housing 40 against an intermediate space 42. The intermediate space 42 adjoins a rolling bearing 43, with which the pivot housing 40 is pivotably mounted in the stationary base frame 30.

[0046] Furthermore, as can be seen in Fig. 3, an axially extended running tooth 135 of the pinion 131 engages with an internal tooth 125 of the second web 122. This forms a so-called splined connection. During operation, the torque or drive power is transmitted via the extended running tooth 135 to the pinion shaft 136 and the pinion 131. To reduce backlash in the overall drive, this splined connection is designed to fit snugly. To prevent the pinion 131 from tilting, a centering element, designed as an interference fit 137, is also provided. During assembly, the second web 122 is heated before being joined to the pinion shaft 136. This is necessary due to the interference fit 137 and also because of the tight fit of the splined connection. The pinion 131 is axially secured in the second web 122 with a screw 129.The second bridge 122 is mounted in the swivel housing 40 together with the pinion shaft 136 by means of two rolling bearings 127 and 128.

[0047] Figure 4 shows a second embodiment of a drive arrangement. In this second embodiment, the connection between the base frame and the swivel housing is reversed compared to the first embodiment shown in Figures 1 to 3. In the second embodiment shown in Figure 4, the first electric motor 100 and the second electric motor 200, as well as the first and second reduction gears 10 and 20, are attached to a stationary base frame 30 of the robot, while the third ring gear 41 is arranged on a swivel housing 40. In this embodiment, the swivel housing 40 is also rotatably mounted on the stationary base frame 30 about a central axis of rotation. The respective first ring gear 113 and the respective second ring gear 123 of the first and second reduction gears 10 and 20 are each attached to the stationary base frame 30.

[0048] The other components of the second embodiment of the drive arrangement 4, in particular the two electric motors 100, 200 and the two reduction gears 10 and 20, can otherwise be designed identically to those of the first embodiment. In particular, the basic design of the two reduction gears 10 and 20, each with a first reduction stage 11, 21 in the form of a first planetary gear set 110, each with a second reduction stage 12, 22 in the form of a second planetary gear set 120, and a third reduction stage comprising a pinion 131, 231, can be designed identically to that of the first embodiment. Therefore, reference is made to the description above regarding the design of these components.In the second embodiment, the aforementioned components are not mounted in the swivel housing 40 as in the first embodiment (ZF Friedrichshafen AG file 306580-WO-PCT, Friedrichshafen, December 2025), but rather in the stationary base frame, i.e., in the robot foot. The output is formed by the third ring gear 41, which is attached to or forms part of the swivel housing 40. The two pinions 131 and 231 engage with the common third ring gear 41, so that the drive power of the two electric motors 100 and 200 is combined at the third ring gear 41.

[0049] Figure 5 illustrates process steps S1-S5 of a method for operating a drive arrangement 1, 4. According to the proposed method, in a first step S1, the first and second electric motors 100 and 200 are driven to pivot the robot arm towards a target position. This means that initially both electric motors 100 and 200 are driven to achieve high acceleration during the pivoting movement of the robot arm. In a further step S2, the second electric motor 200 is switched to generator mode before the target position is reached. This switchover preferably occurs shortly before the target position is reached. The generator mode of the second electric motor 200 produces a braking torque that opposes the drive torque of the first electric motor 100. This decelerates the pivoting movement of the robot arm.Simultaneously, the two drive trains, powered by the first drive motor 100 and the second drive motor 200, become preloaded against each other. This eliminates all backlash in the first reduction gear 10 and the second reduction gear 20, allowing the target position to be approached with high precision. In a third process step S3, the robot arm is moved to its target position by the drive torque of the first electric motor 100 against the braking torque of the second electric motor 200. Steps S1-S3 can be repeated to approach a new target position. The two electric motors 100 and 200 can also be used to hold an achieved target position by applying a torque to each of them such that the two drive trains become preloaded against each other in the target position.

[0050] Using such a method, a so-called master-slave control of the two electric motors 100 and 200 is employed to achieve a low-backlash drive arrangement 1 or 4 even with inexpensive, standard involute gears. (ZF Friedrichshafen AG File 306580-WO-PCT Friedrichshafen 2025-12-05)

[0051] Friedrichshafen 2025-12-05

[0052] Reference sign

[0053] 1 Drive arrangement

[0054] 4 Drive arrangement

[0055] 10 first reduction gear

[0056] 11 first reduction stage

[0057] 12 second reduction stage

[0058] 13 third reduction stage

[0059] 20 second reduction gear

[0060] 21 first reduction stage

[0061] 22 second reduction stage

[0062] 23 third reduction stage

[0063] 30 base frame

[0064] 31 third ring gear

[0065] 40° rotatable swivel housing

[0066] 41 third ring gear

[0067] 42 space

[0068] 43 rolling bearings

[0069] 44 Rotation axis

[0070] 45 Interior

[0071] 100 first electric motor

[0072] 102 Stator

[0073] 103 Rotor

[0074] 104 Connection point for electric motor

[0075] 110 first planetary gear set

[0076] 111 first sun wheel

[0077] 112 first jetty

[0078] 113 first ring gear

[0079] 114 first planetary gears

[0080] 120 second planetary gear set

[0081] 121 second sun wheel

[0082] 122 second jetty

[0083] 123 second hollow gear ZF Friedrichshafen AG File 306580-WO-PCT

[0084] Friedrichshafen 2025-12-05

[0085] 124 Second planetary gears 125 Internal gearing 126 Ring gear component

[0086] 127 rolling bearings

[0087] 128 rolling bearings

[0088] 129 screw

[0089] 131 sprockets

[0090] 135 Running gear 136 Pinion shaft

[0091] 137 Oversize fit 138 Sealing surface

[0092] 139 Seal

[0093] 200 second electric motor 202 stator

[0094] 203 Rotor

[0095] 231 sprocket

[0096] S1-S3 process steps

Claims

ZF Friedrichshafen AG File 306580-WO-PCT Friedrichshafen 2025-12-05 Patent claims 1. Reduction gear (10, 20) comprising a first reduction stage (11, 21), a second reduction stage (12, 22) and a third reduction stage (13, 23), wherein the first reduction stage (11, 21) is designed as a first planet gear set (110), with a driven first sun gear (111), with a first carrier (112) and with a first ring gear (113), wherein first planet gears (114) are mounted on the first carrier (112), each engaging with the first sun gear (111) and the first ring gear (113), wherein the second reduction stage (12) is designed as a second planet gear set (120), with a second sun gear (121), with a second bridge (122) and with a second ring gear (123), wherein second planet gears (124) are mounted on the second bridge (122), which each engage with the second sun gear (121) and with the second ring gear (123), wherein the second sun gear (121) is connected to the first bridge (112) in a twisted manner, wherein the third reduction stage (13) has a pinion (131, 231) which is twisted to the second bridge (122), and wherein the pinion (131, 231) engages in a third ring gear (31, 41), characterized in that that the third ring gear (31) is attached to a stationary base frame (30) or is integrally formed with a stationary base frame (30).

2. Reduction gear (10, 20) comprising a first reduction stage (11, 21), a second reduction stage (12, 22) and a third reduction stage (13, 23), wherein the first reduction stage (11, 21) is designed as a first planet gear set (110), with a driven first sun gear (111), with a first carrier (112) and with a first ring gear (113), wherein first planet gears (114) are mounted on the first carrier (112), each engaging with the first sun gear (111) and the first ring gear (113), wherein the second reduction stage (12) is designed as a second planet gear set (120), with a second sun gear (121), with a second carrier (122) and with a second ring gear (123), wherein second planet gears (124) are mounted on the second carrier (122), which each engage with the second sun gear (121) and with the second ring gear (123), wherein the second sun gear (121) is connected in a twisted manner to the first carrier (112), ZF Friedrichshafen AG File 306580-WO-PCT Friedrichshafen 2025-12-05 wherein the third reduction stage (13) has a pinion (131, 231) which is twisted to the second bridge (122), and wherein the pinion (131, 231) engages in a third ring gear (31, 41), characterized in that that the first and second ring gear (113, 123) are attached to a stationary base frame (30) or are integrally formed with a stationary base frame (30), and that the third ring gear (41) is arranged on a pivot housing (40) that is rotatable relative to the stationary base frame (30) or is integrally formed with the rotatable pivot housing (40).

3. Reduction gear (10, 20) according to claim 1 or 2, characterized in that the third reduction stage (13) has exactly one pinion (131, 231) which engages in the third ring gear (31, 41).

4. Reduction gear (10, 20) according to one of the preceding claims, characterized in that the pinion (131, 231) and the third ring gear (31, 41) are each conically designed, and that adjusting means for adjusting an axial position of the pinion (131, 231) relative to the third ring gear (31, 41) are provided.

5. Reduction gear (10, 20) according to one of the preceding claims, characterized in that a running tooth (135) of the pinion (131, 231) engages in an internal tooth (125) of the second web (122).

6. Reduction gear (10, 20) according to one of the preceding claims, characterized in that the pinion (131, 231) has a pinion shaft (136) which is centered in a bore of the second web (122) by means of an interference fit (137).

7. Drive arrangement (1, 4) for a robot arm of a robot, comprising a first electric motor (100) and a second electric motor (200) as well as a first and a second reduction gear (10, 20), each configured according to one of the preceding claims, wherein the first electric motor (100) is effectively connected to the first sun gear (111) of the first reduction gear (10) in a drive-enhancing manner, wherein the second electric motor (200) is effectively connected to the first sun gear (111) of the second reduction gear (20) in a drive-enhancing manner, and wherein the third ring gear (31, 41) of the first and the second reduction gear (10, 20) is configured as a common third ring gear (31, 41) into which the pinions (131, 231) of the first and second reduction gears (10, 20) engage.

8. Drive arrangement (1) according to claim 7, characterized in that the first and the second reduction gear (10, 20) are arranged at least partially in a common pivoting housing (40) which is rotatable relative to the third ring gear (31), and that the third ring gear (31) is attached to a stationary base frame (30) of the robot.

9. Drive arrangement (1) according to claim 8, characterized in that the first ring gear (113) and the second ring gear (123) are rigidly arranged in the pivot housing (40).

10. Drive arrangement (1) according to claim 7 or 8, characterized in that an outer circumferential surface of the third ring gear (31) is designed as a sealing surface (138), and that a seal (139) is arranged on the sealing surface (138) to seal an interior (45) of the swivel housing (40) against an intermediate space (42), wherein the intermediate space (42) adjoins a rolling bearing (43) with which the swivel housing (40) is rotatably mounted in the stationary base frame (30).

11. Drive arrangement (4) according to claim 7, characterized in that the first and second electric motors (100, 200) and the first and second reduction gears (10, 20) are attached to a stationary base frame (30) of the robot, and that the third ring gear (31, 41) is arranged on a swivel housing (40) which is rotatable relative to the base frame (30).

12. Method for operating a drive arrangement (1, 4) according to one of claims 7 to 11 comprising the following steps: - Motorized driving (S1) of the first and second electric motors (100, ZF Friedrichshafen AG File 306580-WO-PCT Friedrichshafen 2025-12-05 200) to pivot the robot arm towards a target position, - Switching (S2) of the second electric motor (200) to generator operation before the target position is reached, - Moving the robot arm to the target position (S3) by the drive torque of the first electric motor (100) against the braking torque of the second electric motor (200).

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