WO2025040883A1

WO2025040883A1 - Improvements relating to robotic apparatus

Info

Publication number: WO2025040883A1
Application number: PCT/GB2024/052152
Authority: WO
Inventors: Kartikeya WALIA; Philip BREEDON
Original assignee: Nottingham Trent University
Current assignee: Nottingham Trent University
Priority date: 2023-08-22
Filing date: 2024-08-15
Publication date: 2025-02-27
Anticipated expiration: 2026-02-22
Also published as: GB2632831A; GB202312821D0

Abstract

A ring gear (10) is described. The ring gear (10) has: a first meshing formation (12) provided around an inner circumference of the ring gear (10); and a second meshing formation (22) comprising longitudinally extending merlons (24). A part for a robotic apparatus (100), assembly (400) and robotic apparatus including the ring gear (10) are also described.

Description

IMPROVEMENTS RELATING TO ROBOTIC APPARATUS

Technical Field of the Invention

The present invention relates to a ring gear, as well as a part, an assembly and robotic apparatus incorporating the ring gear.

Background to the Invention

Some prior robotic manipulators (for use in medical or industrial settings) are modular so that modular parts of those manipulators can be repaired/replaced so that the whole manipulator does not need to be replaced in the case of a failure of a single component of such manipulators. The modular manipulators generally include rotatable sections.

The prior modular manipulators are not easily customised and are often difficult to disassemble. Furthermore, often the design of these modular manipulators is not very robust for reliable performance and does not allow the use of off the shelf components. In particular, often complex arrangements with expensive custom-made parts are required to transmit torque from actuators to other moving parts of those manipulators.

It is an object of the present invention to obviate or mitigate at least one problem with prior modular manipulators.

Summary of the Invention

According to a first aspect of the present invention, there is provided a ring gear having: a first meshing formation provided around an inner circumference of the ring gear; and a second meshing formation comprising longitudinally extending merlons.

The ring gear of the present invention enables a simplified transmission arrangement between a motor and a rotating part of a modular robotic apparatus. The specific transmission is very easy to disassemble, allowing very easy maintenance and customisation of an arrangement incorporating the ring gear. Furthermore, the transmission arrangement is very robust, thereby enabling a harder wearing and stronger manipulator. Furthermore, and very advantageously, the specific transmission allows use of off the shelf components (such as off the shelf motors), thereby massively reducing the cost of producing a manipulator incorporating the ring gear. Further, it is easier to obtain those off the shelf components, reducing the time a manipulator in need of repair is out of action. The ring gear also ensures proper alignment of rotating parts of a robotic apparatus.

The first meshing formation may comprise ridges and channels. The channels may be located between the ridges. The first meshing formation may extend around the whole inner circumference of the ring gear. The first meshing formation may be for meshing with a first corresponding meshing formation. The first meshing formation may be for meshing with a gear.

The first meshing formation may be a herringbone formation. The ridges and channels may be V-shaped.

The herringbone formation provides a large total contact ratio, and a high load carrying capacity. It also enables a direct drive mechanism between a motor and a pinion gear engaging the first meshing formation to be utilised, making a manipulator incorporating the ring gear more compact.

The ring gear may have a curved outer surface extending around an outer circumference of the ring gear. The curved outer surface may describe a circle.

The ring gear may comprise an annular flange that projects outwardly from a remaining portion of the ring gear in a radial direction. The annular flange may comprise the curved outer surface.

The annular flange allows a specific retention arrangement for keeping the ring gear inside a hollow part incorporating the ring gear to be utilised. The specific retention arrangement is particularly easy to assemble and disassemble.

The second meshing formation may be for meshing with a second corresponding meshing formation. The merlons may be regularly arranged around a central longitudinal axis of the ring gear. The merlons may comprise at least five merlons. The merlons may be unapertured (in other words, the merlons may lack apertures). All the merlons may extend the same longitudinal distance. The merlons may be arranged in a ring. The merlons may be arranged in the ring around the central longitudinal axis of the ring gear.

The second meshing formation may comprise crenels between the merlons. Each merlon may have a distal end and each merlon may taper inwardly to the distal end. Each merlon may taper inwardly in a longitudinal direction. The distal end may be planar. Each merlon may comprise side surfaces that extend to the distal end. The side surfaces may be planar. Each side surface may be inclined. Each crenel may be configured to receive a merlon from the second corresponding meshing formation.

The merlons may be substantially trapezoidal in shape (i.e., each merlon may describe the majority of a trapezoid). The distal end and side surfaces may define the substantially trapezoidal shape. Alternatively, the merlons may be substantially rectangular in shape (i.e., each merlon may describe the majority of a rectangle).

The ring gear may comprise an outer circumferential groove. The outer circumferential groove may be for receiving an elastomeric ring.

The second meshing formation may be provided at an end of the ring gear.

The ring gear may extend longitudinally between first and second ends thereof. The second meshing formation may be provided at the first end of the ring gear. The annular flange may be spaced apart from the first and second ends of the ring gear. The outer circumferential groove may be located between the annular flange and the first end of the ring gear.

The ring gear may comprise a flat edge upon which the ring gear may rotate. The annular flange may comprise the flat edge.

The ring gear may be formed from a self-lubricating polymer.

According to a second aspect of the present invention, there is provided a part for a robotic apparatus comprising: a hollow body having an opening; a ring gear according to the first aspect at least partially located inside the hollow body; and a pinion gear meshed with the first meshing formation so that the pinion gear can rotate the ring gear.

The part enables torque to be transferred from a motor to a rotating part of a modular robotic apparatus. There are numerous advantages associated with the part of the present invention, for example, the part is easy to disassemble and assemble, and has a high torque amplification. Furthermore, the part is easily customised, has a robust construction and can me more lightweight as a more simplified motor may be used.

The hollow body with an opening permits cables/fluid lines to be run internally through the part, thereby negating the need for externally run cables/fluid lines, which limit joint motions. Prior externally run cables often break during use of prior arrangements.

The part may comprise a retention arrangement for retaining the ring gear within the body. The retention arrangement may comprise a split ring arranged to retain the ring gear within the body. The split ring may be resiliently deformable and configured to return to a rest state when compressed. The split ring may be compressed when it is arranged to retain the ring gear within the hollow body.

The ring gear may comprise an annular flange and the annular flange may be seated on a ledge within the body. The ledge may be annular. The annular flange may comprise a first edge which is seated on the ledge and a second edge opposing the first edge. The body may comprise a split ring groove, which may be substantially annular. The split ring may be fitted into the split ring groove such that a portion of the split ring extends over the second edge of the annular flange to retain the ring gear within the body. The split ring may be snap-fitted into the split ring groove. The split ring groove may be located above the ledge.

The retention arrangement for retaining the ring gear inside the hollow body is particularly easy to assemble and disassemble, reducing the time to perform maintenance/repair operations. Also, less skilled workers may perform those operations.

The split ring may be substantially shaped like a ring but have two free ends separated by a narrow gap. The part may further comprise a hollow guard located within the body. The hollow guard may be located inside the ring gear. The hollow guard may have a passage for one or more fluid lines or cables extending therethrough. The hollow guard may have a curved surface that partially extends around the pinon gear. The hollow guard may be fixed in position within the body. The cable guard prevents the pinching of the cables/fluid lines between the gear meshing.

The part may further comprise a motor arranged to drive the pinion gear. The motor may be located within the hollow body. A direct drive mechanism may mechanically connect the motor with the pinion gear.

The first meshing formation of the ring gear may be a herringbone formation and the pinion gear may have a suitable formation for meshing with the herringbone formation.

The pinion gear may be located within the body.

The ring gear may be retained within the body such that the ring gear can rotate about a ring gear rotation axis. The ring gear rotation axis may be co-axial with an opening axis of the opening of the body. The pinon gear may rotate about a pinion gear rotation axis that is co-directional with the ring gear rotation axis.

The ring gear may be partially located within the body such that at least the merlons of the second meshing formation of the ring gear are provided beyond a hollow body end of the body comprising the opening. The hollow end of the body and the ring gear may be radially separated by an annular gap.

The ring gear, pinion gear and/or split ring may be formed from a selflubricating polymer.

The part of the second aspect may comprise all or some of the features of the ring gear of the first aspect as desired or appropriate.

According to a third aspect of the present invention, there is provided an assembly comprising: a first part in accordance with the second aspect; a second part with a second body and a second corresponding meshing formation meshed with the second meshing formation of the ring gear such that a substantially annular groove is formed between the hollow body and the second body; and an annular clamping element located in the annular groove.

The assembly enables torque to be transferred from a motor to a rotating part of a modular robotic apparatus. There are numerous advantages associated with the assembly of the present invention, for example, the assembly is easy to disassemble and assemble, and has a high torque amplification. The number of meshing teeth in the gears can be customised to achieve desired torque amplification. Furthermore, the assembly is easily customised, has a robust construction and can be more lightweight as a more simplified motor may be used. The assembly also ensures proper alignment of rotating parts of the assembly. These consolidated parts offer a reduction in potential part failures due to less friction and part misalignment over time, reduced assembly errors by increasing simplicity of the assembly process and lower production costs.

The annular clamping element may be arranged to hold the second meshing formation of the ring gear in meshing engagement with the second corresponding meshing formation of the second part. The annular clamping element may comprise two substantially semi-circular elements held together by one or more fasteners.

At least one elastomeric ring may be located in the annular groove. The annular clamping element may comprise at least one elastomeric ring groove and the at least one elastomeric ring may be received in the at least one elastomeric ring groove. The at least one elastomeric ring may be biased against one or more of the second and second corresponding meshing formations. Preferably, the assembly comprises first and second elastomeric rings located in the annular groove, and the first elastomeric ring extends around the second mating formation and the second elastomeric ring extends around the second corresponding mating formation, wherein the annular clamping element comprises first and second elastomeric ring grooves that receive the first and second elastomeric rings, respectively. The second body may be hollow. The second body may comprise a second opening. The hollow body, the meshed second meshing and second corresponding meshing formations, and second body may form a passageway. The passageway may be configured so that at least one cable or fluid line can extend through the passageway. The passage defined by the hollow guard may be located in the passageway. The assembly may comprise the at least one cable or fluid line and the at least one cable or fluid line may extend through the passageway.

The first part may comprise a hollow body end and the first meshing formation may be provided at least partially beyond the hollow body end. The second part may comprise a second body end and the second corresponding meshing formation may be provided at least partially beyond the second body end. The hollow body end and second body end may at least partially form sidewalls of the annular groove. The second meshing formation and corresponding second meshing formation may form an intermediate wall between the sidewalls. The sidewalls and the intermediate wall may define the annular groove.

The assembly of the third aspect may comprise all or some of the features of the ring gear of the first aspect or the part of the second aspect as desired or appropriate.

According to a fourth aspect of the present invention, there is provided a robotic apparatus comprising: the assembly of the third aspect; and a tool mounted directly or indirectly to the second part.

The tool may be a grabber tool.

The robotic apparatus may be modular.

The apparatus of the fourth aspect may comprise all or some of the features of the ring gear of the first aspect, the part of the second aspect or the assembly of the third aspect as desired or appropriate.

Detailed Description of the Invention In order that the invention may be more clearly understood one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1 shows an exploded view of a part for a robotic apparatus according to a first embodiment of the present invention;

Figure 2 shows a detail view of a ring gear according to the present invention, which is shown in Figure 1;

Figure 3 shows an unexploded partial view of the part of Figure 1;

Figure 4 shows an exploded view of a part for a robotic apparatus according to a second embodiment of the present invention;

Figure 5A shows an unexploded view of the part of Figure 4 but rotated with respect to its position in Figure 4;

Figure 5B shows a partial sectional view of a retention arrangement utilised in the first and second embodiments;

Figure 6 shows a part for a robotic apparatus according to a third embodiment of the present invention;

Figure 7 is a schematic of an assembly according to the present invention; and

Figures 8 A to 8E shows schematically the formation of the assembly of Figure 7.

Referring now to Figure 1, there is shown a part 100 for a robotic apparatus according to a first embodiment of the present invention. The part 100 includes a ring gear 10 at least partially located within a hollow body 102 of the part 100 (when the part is fully assembled).

The part 100 will be described in full below. However, referring now to Figure 2, the ring gear 10 is shown in detail. As shown the ring gear 10 generally has the form of a short hollow cylinder with a central bore extending therethrough and a curved outer surface 13 extending around an outer circumference of the ring gear 10. The curved outer surface 13 preferably describes a circle. The ring gear 10 has a first meshing formation 12 provided around its inner circumference. The first meshing formation is for meshing with a gear (preferably a pinion gear) and comprises ridges 14 and channels 16 between the ridges 14. In the depicted, example the first meshing formation is a herringbone formation, which enables a high torque amplification. The ridges 14 are therefore V-shaped elements and the channels 16 are V-shaped slots between the V-shaped elements.

The ring gear 10 extends between first and second ends 18, 20 thereof and includes a second meshing formation 22 provided at the first end 18 of the ring gear. The second meshing formation includes longitudinally extending merlons (or teeth) 24. The second meshing formation 22 is arranged to mesh with a second corresponding meshing formation of a separate element (not shown). As shown the merlons 24 are arranged in a ring and are regularly arranged (or distributed) around a central longitudinal axis of the ring gear. Preferably, there are at least five merlons 24. However, in the depicted example there are twelve merlons. For ease of viewing for the reader, not all merlons 24 have been allocated a reference numeral in Figure 2.

Each merlon 24 is solid (i.e., unapertured) and comprises a planar distal end 26 and each merlon 24 tapers inwardly to the distal end in a longitudinal direction. In the depicted example, each merlon 24 has a pair of inclined side surfaces 25 that extend to the distal end 26. The merlons depicted a generally trapezoidal in shape (i.e., describe the majority of a trapezoidal shape), although other shapes are suitable such as a rectangular shape. Other shapes are possible but trapezoidal shape allows for easier alignment during assembly. In particular, the distal end 26 and side surfaces 25 may define the substantially trapezoidal shape. The merlons 24 are preferably separated by crenels 28 and each crenel 28 is arranged to receive the merlon 24 of a corresponding second meshing formation. Like the merlons 24, the crenels 28 of the depicted example are also generally trapezoidal in shape.

The ring gear 10 also includes an annular flange 30 which projects outwardly from a remaining portion 32 of the ring gear 10, and comprises first and second opposing edges 34, 36 and a cylindrical surface 13 (also the curved outer surface described above) that connects the first and second edges. The first edge 34 is a flat edge upon which the ring gear 10 may rotate. The annular flange is preferably spaced from the first and second ends 18, 20 of the ring gear.

The ring gear 10 also includes an outer circumferential groove 38 that is formed in the outer surface of the ring gear 10 and is for receiving an elastomeric ring. The outer circumferential groove 38 is located between the annular flange 30 and first end 18 of the ring gear 10.

The ring gear 10 is preferably formed of a self-lubricating polymer. However, the ring gear may alternatively be used with a lubricant and formed from metal.

Referring back to Figure 1, the part 100 for a robotic apparatus according to a first embodiment of the present invention will now be described in full. The specific part 100 of Figure 1 is preferably a base joint of a robotic apparatus and comprises a hollow body 102 comprising a substantially tubular housing 104 closed at one end by a base plate 106 and open at a hollow body end 108. Specifically, the hollow body end 108 comprises a substantially circular opening 110.

As best shown in Figure 3, the ring gear 10 is at least partially located within the body such that at least the merlons 24 of the second meshing formation are provided beyond the hollow body end 108 of the body. Preferably, an annular gap 109 radially separates the hollow body end 108 and the ring gear 10.

Referring back to Figure 1, the ring gear 10 is retained within the body 102 by a split ring 111 as will be described in detail in relation to Figure 5B. The split ring 111 may be resiliently deformable and configured to return to a rest state when compressed. The split ring 111 may be compressed when it is arranged to retain the ring gear 10 within the hollow body 102.

The ring gear 10 is retained within the hollow body 102 such that it may rotate about a ring gear rotation axis that is co-axial with an opening axis of the circular opening 110. As best shown in Figure 3, the first meshing formation 12 of the ring gear 10 is meshed with a pinion gear 112 that is located within the body 102. In the example depicted in Figure 3, both of the ring and pinion gears 10, 112 have cooperating herringbone formations. The pinion gear 112 is driven by a motor 114 that is fixed to a supporting frame 116 within the hollow body 102. Preferably, a direct drive mechanism mechanically connects the motor 114 with the pinon gear 112, and the motor is arranged to rotate the pinion gear 10 about a pinion gear rotation axis that is co-directi onal with the ring gear rotation axis.

The part 100 may also comprise an elastomeric ring 124 that is arranged to fit into the outer circumferential groove 38 that is formed in the outer surface of the ring gear 10.

Also shown in Figure 1 is an annular clamping element 130 for assisting in connecting the part 100 of Figure 1 to another part of an assembly. The assembly will be described in greater detail below in relation to Figure 7. The clamping element 130 shown in Figure 1 comprises two substantially semi-circular elements 132 connected by two fasteners 134.

Located inside the ring gear 10 and the body 102 is a hollow guard 120 that prevents cables/fluid lines run through the part from becoming damaged/caught by the pinon/ring gears 112, 10. The hollow guard 120 has a passage 122 for the cables/fluid lines and comprises a curved surface 123 that partially extends around and substantially corresponds to an outer surface of the pinion gear 112.

Referring now to Figure 4, there is shown a part 200 for a robotic apparatus according to a second embodiment of the present invention. The part 200 of the second embodiment is an arm joint for a modular robot and is couplable to other parts at ends thereof. Like the first embodiment, the part includes a hollow body 102, ring gear 10, pinion gear 112, motor 114 and hollow guard 120 (the same reference numerals for these elements as used in Figure 1 have been used in Figure 4). The open ends 202 have openings 204 that are substantially orthogonal to each other. The body 102 also includes a removable cap 206 that can be removed to allow additional access to an interior of the body.

Referring to Figure 5 A, the part 200 of Figure 4 is shown in an unexploded view without its removable cap and rotated with respect to its position in Figure 4. A detail and part sectional view of a retention arrangement for retaining the ring gear 10 within the hollow body 102 is shown in Figure 5B. This retention arrangement is also utilised in the first embodiment, although not shown in Figures 1 and 3. As shown the annular flange 30 of the ring gear 10 is seated on an annular ledge 138 within the body 102. Specifically, the annular flange 30 comprises first and second opposing edges 34, 36 and the first opposing edge 34 is seated on the ledge 138. The body 102 comprises a split ring groove 144, which is substantially annular, and located above the ledge 138. The split ring I l l is fitted into the split ring groove 144 such that a portion of the split ring 111 extends over the second opposing edge 36 of the annular flange 30 to retain the ring gear 10 within the body 102. The annular gap 109 allows the split ring groove 144 to be accessed and preferably the split ring 111 is snap-fitted into the split ring groove 144.

Referring now to Figure 6, there is shown a part 300 for a robotic apparatus according to a third embodiment of the present invention. The part 300 of the third embodiment is a wrist joint for a modular robot and is couplable to other parts at ends thereof, like the second embodiment. Like the first embodiment, the part includes a hollow body 102, ring gear 10, pinion gear 112, motor 114 and cable guard 120 (the same reference numerals for these elements as used in Figure 1 have been used in Figure 6). Like the second embodiment, the open ends 202 of the third embodiment have openings 204 that are substantially orthogonal to each other. A significant difference between the third embodiment and the second embodiment is that the body 102, ring gear 10 and pinion gear 112 are smaller. The ring gear 10 also only has five merlons 24. The part of the third embodiment also does not utilise a split ring.

Referring now to Figure 7, which shows a schematic diagram of an assembly

400 according to the present invention. The assembly 400 comprises first and second parts 401, 406, where the first part 401 is a part in accordance with the embodiments of a part for a robotic apparatus described above. The first part 401 is indicated by item

401 in Figure 7. Figure 7 shows the part 401 as a single item. However, it should be appreciated that, like the embodiments 100, 200 and 300 described above, the part 401 includes a hollow body 102 and a ring gear 10 fitted into that hollow body such that the merlons 24 of the second meshing formation 22 of the ring gear are provided beyond the hollow body end 108 of the hollow body 102 and the ring gear 10 can rotate. The first part includes a first elastomeric ring 402, which is preferably located in the outer circumferential groove of the ring gear. The second part 406 has a second corresponding meshing formation 408, and a second body 410 with a second body end 412. The second corresponding meshing formation 408 has merlons 424 provided beyond the second body end 412 of the second body 410. The second corresponding meshing formation and second body 410 are preferably integrally formed. The second body 410 is preferably hollow and the second corresponding meshing formation 408 defines a second opening which allows access to an interior of the second body. Preferably, and as shown, the second part 406 includes a second elastomeric ring 418.

The second and corresponding second meshing formations 22, 408 are in meshing engagement such that an annular groove 424 is formed between the hollow body 102 and second body 410. In particular, the hollow body end 108 and second body end 412 at least partially define sidewalls of the annular groove 424 and the second meshing and the corresponding second meshing formations 22, 408 form an intermediate wall of the annular groove that is between the sidewalls.

An annular clamping element 130 arranged to hold the meshing formations 22, 408 in meshing engagement is located in the annular groove 424. The annular clamping element 130 has first and second elastomeric ring grooves 452, 454 that receive the first and second elastomeric rings 402, 418, respectively. The first and second bodies 102, 410 and engaged second meshing and corresponding second meshing formations 22, 408 form a passage through which cables/fluid lines may be run.

With reference to Figures 8 A to 8E, how the assembly of Figure 7 is assembled will now be described.

Firstly, as shown in Figure 8A, the first part 401 is assembled (i.e., by fitting the ring gear 10 into the hollow body 102 such that it is retained therein and can rotate).

Then, as shown in Figure 8B, the first elastomeric ring 402 is fitted over the ring gear 10.

As shown in Figure 8C, then the second part 406 having a second corresponding meshing formation 408 is then brought close to the first part 401. Preferably, and as shown, the second elastomeric ring 418 is fitted over the second corresponding meshing formation 408 before the second part 406 is brought close to the first part 401. As shown in Figure 8D, the first and second parts 401, 406 are then brought together such that the second meshing formation 22 of the ring gear is in meshing engagement with the second corresponding meshing formation 408 of the second part 406, and the annular groove 424 between the hollow body 102 and the second body 410 is formed.

As shown in Figure 8E, then annular clamping element 450 is located in the annular groove 424 so that the annular clamping element 450 holds the second meshing formation 22 and second corresponding meshing formation 408 in meshing engagement to form the assembly 400.

The assembly shown in Figure 7 may be incorporated in a modular robotic apparatus, and a tool, such as a grabber tool, may be attached to the second part. Torque from a motor may be transferred to the second part via the ring gear.

The ring gear, part and assembly of the present invention provide a simplified transmission arrangement between a motor and a rotating part of a modular robotic apparatus. The specific transmission is very easy to disassemble, allowing very easy maintenance and customisation of an arrangement incorporating the ring gear. The transmission arrangement is very robust, thereby enabling a harder wearing and stronger manipulator.

Very advantageously, the specific transmission allows use of off the shelf components (such as off the shelf motors), thereby massively reducing the cost of producing a manipulator incorporating the ring gear. Further, it is easier to obtain those off the shelf components, reducing the time a manipulator in need of repair is out of action. The ring gear also ensures proper alignment of rotating parts of a robotic apparatus.

The hollow body with an opening permits cables/fluid lines to be run internally through the part, thereby negating the need for externally run cables/fluid lines, which limit joint motions.

The one or more embodiments are described above by way of example only. Many variations are possible without departing from the scope of protection afforded by the appended claims.

Claims

1. A ring gear having: a first meshing formation provided around an inner circumference of the ring gear; and a second meshing formation comprising longitudinally extending merlons.

2. The ring gear of claim 1, wherein the first meshing formation comprises ridges and channels.

3. The ring gear of claim 1 or 2, wherein the first meshing formation is a herringbone formation.

4. The ring gear of claim 3 when dependent on claim 2, wherein the ridges and channels are V-shaped.

5. The ring gear of any preceding claim, wherein the ring gear comprises an annular flange that projects outwardly from a remaining portion of the ring gear in a radial direction.

6. The ring gear of any preceding claim, wherein the merlons are regularly arranged around a central longitudinal axis of the ring gear.

7. The ring gear of any preceding claim, wherein the merlons comprise at least five merlons.

8. The ring gear of any preceding claim, wherein the merlons extend the same longitudinal distance.

9. The ring gear of any preceding claim, wherein the merlons are arranged in a ring.

10. The ring gear of any preceding claim, wherein the second meshing formation comprises crenels between the merlons.

11. The ring gear of claim 10, wherein each crenel is configured to receive a merlon from a second corresponding meshing formation.

12. The ring gear of any preceding claim, wherein each merlon has a distal end and each merlon tapers inwardly to the distal end.

13. The ring gear of claim 12, wherein the distal end is planar.

14. The ring gear of any preceding claim, further comprising an outer circumferential groove.

15. A part for a robotic apparatus comprising: a hollow body having an opening; a ring gear according to any preceding claim at least partially located inside the hollow body; and a pinion gear meshed with the first meshing formation so that the pinion gear can rotate the ring gear.

16. The part of claim 15, wherein the part comprises a split ring arranged to retain the ring gear within the body.

17. The part of claim 16, wherein the ring gear is the ring gear of claim 5 and the annular flange of the ring gear is seated on a ledge within the body.

18. The part of claim 17, wherein the annular flange comprises a first edge which is seated on the ledge and a second edge opposing the first edge, wherein the body comprises a split ring groove, and the split ring is fitted into the split ring groove such that a portion of the split ring extends over the second edge of the annular flange to retain the ring gear within the body.

19. The part of claims 15 to 18, further comprising a hollow guard located within the body.

20. The part of claim 19, wherein the hollow guard is located inside the ring gear.

21. The part of any of claims 15 to 20, further comprising a motor arranged to drive the pinion gear.

22. An assembly comprising: a first part in accordance with any of claims 15 to 21; a second part with a second body and a second corresponding meshing formation meshed with the second meshing formation of the ring gear such that a substantially annular groove is formed between the hollow body and the second body; and an annular clamping element located in the annular groove.

23. The assembly of claim 22, wherein at least one elastomeric ring is located in the annular groove, wherein the annular clamping element comprises at least one elastomeric ring groove and the at least one elastomeric ring is received in the at least one elastomeric ring groove.

24. The assembly of claim 22 or 23, wherein the second body is hollow, wherein the second body comprises a second opening, wherein the hollow body, the meshed second meshing and second corresponding meshing formations, and second body form a passageway.

25. A robotic apparatus comprising: the assembly of any of claims 22 to 24; and a tool mounted directly or indirectly to the second part.