The present invention relates to articulated joints and, in particular, those suitable for robotic arms.

The inventor has previously developed an electrical connector for communicating electrical signals via a joint such as a ball and socket joint. This has been shown in WO2016/009365 and in GB1701044.8, each of which is incorporated herein by reference. The inventor has subsequently realised that the connector provides a stable joint that is not only suitable for incorporation into a robot arm, but particularly suitable for use as a repeated unit is a robot arm that may flex about two arms at multiple locations along its length.

For a better understanding of the invention and to show how the same may be put into effect, reference is now made, by way of example only, to the accompanying drawings in which:

Figure 1 shows a side view of a first embodiment of a joint for a robot arm;

Figure 2 shows an end view of the joint of Figure 1 ;

Figure 3 shows an exploded view of the joint of Figure 1 ;

Figure 4 shows a perspective view of the joint of Figure 1 when articulated;

Figure 5 shows a robot arm formed of multiple articulated joints of the types shown in Figure 1 ;

Figure 6 shows a side view of a second embodiment of a joint for a robot arm;

Figure 7 shows a cut-away perspective view of a third embodiment of a joint for a robot arm, with a sub-view showing the complete joint;

Figure 8 shows an exploded view of the joint of Figure 7;

Figure 9 shows a perspective view of the joint of Figure 7 when articulated;

Figure 10 shows a robot arm formed of multiple articulated joints of the type shown in

Figure 7;

Figure 1 1 shows a schematic representation of a control system for a robot arm;

Figure 12 shows an arm segment;

Figure 13 shows an alternative ball portion for an electrical connector;

Figure 14 shows a further alternative ball portion for an electrical connector;

Figure 14A shows an alternative socket portion for use with the alternative ball portion of

Figure 14;

Figure 14B shows the ball portion of Figure 14 inserted in the socket portion of Figure 14A Figure 15 shows a top view of the ball portion of Figure 14;

Figure 15A shows a top view of the socket portion for of Figure 14A;

Figure 15B shows a top view of the ball portion and socket portion of Figure 14B;

Figure 16 shows a side view of the ball portion of Figure 14; and

Figure 17 shows a cross-section of the ball portion of Figure 14.

Figure 1 shows a first embodiment of a joint 100 for a robot arm 1000 in accordance with the invention. The joint 100 is formed from two engaged arm segments 10. Each arm segment 10 has a connector 12, 14 at one or each end. A single arm segment 10 in isolation is shown in Figure 12. That embodiment also shows an optional housing around the arm segment 10.

In Figure 1 , the first arm segment 10 has a first connector 12 at one end 10a, while the second arm segment 10 has a second connector 14 at one end 10b. The first connector 12 is engaged with the second connector 14 to form the joint 100. The joint 100 allows rotation of one arm segment relative to the other. By this rotation, the longitudinal axes of each arm segment 10 may be angled relative to one another in at least two degrees of freedom (that is to say that the at least two degrees of freedom of rotation do not include rotation of an arm segment about its own axis X, Y). The joint 100 is shown with the two arm segments 10 aligned along common longitudinal axis X in Figure 1. Figure 4 shows the arm segments angled such that longitudinal axis X of the first arm segment 10 does not coincide with longitudinal axis Y of the second arm segment 10. Thus, the joint 100 may therefore act like a ball and socket joint.

As can be seen from Figures 2 and 4, the second connector 14 may have an end cap 16 that prevents detachment of the first connector 12 therefrom. The end cap has an aperture with a diameter less than the width of the first connector 12. Preferably, each of the arm segments 10 has a first connector 12 at one end and a second connector 14 at the opposite end so as to define a repeating unit in which the electrical contacts 18 of the first connector are connected to the electrical contacts 17 of the second connector 14 via a connection portion to thereby enable communication along the arm segment 10. Multiple repeating units may be combined to form a robot arm 1000 as shown in Figure 5. In the first embodiment, the first connector 12 is a male member and the second connector 14 is a female member. Preferably, the first connector 12 is substantially spherical

(optionally, with grooves or teeth formed in its outer surface) or is formed from multiple arcuate members that collectively define an outer spherical surface, and the second connector 14 has a complementary concave hemispherical surface, or a surface that forms part of a hemispherical surface, (optionally, with grooves or projections formed therein) for receiving the first connector 12. In this way, joint 100 may form or include a ball and socket joint.

Each arm segment 10 can be formed of two or more separable members. For example, as shown in the figures, the arm segment 10 may comprise a first part terminating in a sleeve 15. The sleeve 15 may be fitted into, fitted over, or otherwise engaged with a

corresponding second part of the arm member 10 to form a single arm segment 10 with a first connector 12 at one end 10a and a second connector 14 at the other end 10b.

The first connector 12 comprises one or more first electrical contact(s) 18. In the example shown in Figure 1 , the first connector 12 comprises a plurality of first electrical contact(s) 18.

The second connector 14 comprises one or more second electrical contact(s) 17. Each of the first electrical contacts 18 is in electrical communication with a corresponding one of the second electrical contacts 17. As will be described below, the joint 100 is arranged such that the electrical connection between corresponding contacts 17, 18 is maintained irrespective of the angle between the longitudinal axes X, Y of the neighbouring arm segments 10.

The joint 100 also comprises a set of two or more actuators 20 for moving the first arm segment 10 relative to the second arm segment 10. Preferably, at least three actuators 20 are provided for each joint 100. In the first embodiment, a set of three actuators 20a, 20b, 20c are provided for the joint 100. The set of actuators 20 may be provided at one end 10a. 10b of an arm segment 10 for use with a single joint 100. Whilst the actuators 20 are physically engaged with both arm segments 10 of each joint 100, they are preferably electrically connected to one of the arm segments 10 for the purpose of control (as discussed below). In this first embodiment, the actuators 20 are linear actuators. The actuators 20 are arranged to extend between one or more first framework(s) 22a rigidly connected to the first arm segment 10 and one or more second framework(s) 22b rigidly connected to the second arm segment 10. Each framework 22a, 22b provides a connection point 24 for an actuator 10, with the connection points 24 equally spaced around the longitudinal axis X, Y of the respective arm portion 10. The actuators 20 may be pivotally mounted to the frameworks 22a, 22b at the connection points 24. For each actuator 20, at least one connection point 24, and preferably both connection points 24, is formed as a ball and socket joint. Optionally, for each actuator 20, one connection point 24 is a hinge joint and the other is a ball and socket joint.

As can be seen from Figure 4, the actuators 20a, 20b, 20c, may be differentially actuated to control the orientation of the first arm segment 10 relative to the second arm segment 10.

As can be seen from Figure 6, a second embodiment of a joint 200 in accordance with the invention has largely the same structure as that of the joint 100 of the first embodiment. However, in the second embodiment the second framework 22b of the first embodiment is not provided. Instead the linear actuators 20 are mounted directly onto the second connector 14.

Irrespective of the structure to which they are mounted, in both first and second

embodiments, the linear actuators 20 are mounted such that extension or retraction thereof can vary the angle between the longitudinal axes X, Y of the two arm segments 10.

As can be seen from Figures 7 to 9, a third embodiment of a joint 300 in accordance with the invention has a similar structure to that of the joint 100 of the first embodiment.

The third joint 300 is not articulated by linear actuators 20, but by motors 320 (although, a combination of the two types of actuator is possible). Each of the motors 320 is arranged to rotate a drive gear 325, which is preferably a worm gear. Each of the drive gears 325 is arranged to engage a corresponding arcuate track 50 formed with a plurality of teeth spaced along its length. The arcuate tracks 50 together lie on the surface of a sphere. It is preferred for the first member 12 to be formed generally as a sphere, with the arcuate tracks 50 generally corresponding to its outer surface.

For example, the first connector 12 may be formed of a plurality of arc-shaped toothed inserts to form the tracks 50.

As with the earlier embodiments, there are at least two actuators 320, and most preferably three or more. The tracks 50 are preferably equally spaced about the longitudinal axis X of the first connector and the actuators 320 correspondingly spaced around the longitudinal axis Y of the second connector 14. Each track 50 preferably defines an arc along which it may engage with the corresponding drive gear that lies in a plane extending through the longitudinal axis X of the first arm segment 10.

Each motor 320 is pivotally mounted on the second arm segment 10 (most preferably on the second connector 14). Each motor 320 preferably includes a housing 326 by which it is pivotally mounted on the second arm segment 10. Each motor 320 or its housing 326 may include an elongate projection 330 that engages in a groove 55 that extends in parallel with the track 50. The elongate projection 330 engages the groove 55 such that during rotation of the first connector 12 relative to the second connector 14, the alignment of each motor 320 with its corresponding track 50 is maintained.

As one of the motors 320a is driven to rotate, the drive gear rotates and thereby drives along the teeth of the corresponding arcuate track 50a so as to engage with a different location thereof. This forces the first connector 12 to rotate, thereby changing the angle between the longitudinal axes X, Y. As the angle changes, the elongate projections 320b, 320c follow the motion of the grooves 50b, 50c, thereby rotating the corresponding motors 320b, 320c about their pivotal mountings. In this way, the drive gears of the other motors 320b, 320c stay in engagement with their corresponding tracks 50b, 50c.

Whereas in the first and second embodiments, the first connector 12 preferably contacts a hemispherical surface of the second connector 14, or a surface that forms part of a hemispherical surface, so that any loads may be born by that contact, in the third embodiment 300 the load-bearing contact may be between the drive gears 325 and the tracks 50. Optionally, further support may be provided via supporting surfaces (not shown) of the second connector 14 arranged to engage the first connector 12 in the areas 52 between the tracks 50.

Furthermore, as shown in the sub-view of Figure 7, a housing 325 may be provided as part of connector 14. The housing 325 may include or contain the supporting surfaces. The housing 325 may include or contain the supporting surfaces. The housing 325 may also prevent the disengagement of the first and second connectors 12, 14.

Figure 5 shows a robot arm 1000 formed as a chain of multiple articulated joints 100w, 10Ox, 10Oy, 10Oz. As can be seen from Figure 5, each joint 100 can be individually articulated by controlling the actuators 20a, 20b, 20c extending across that joint 100.

In Figure 10, there is shown another robot arm 3000. Whereas the robot arm 1000 of Figure 5 includes multiple repeating units of the type shown in Figure 1 , the Figure 10 embodiment includes multiple repeating units of the type shown in Figure 6.

The robot arm 1000, 3000 may comprise a first, second, and third arm segment A, B, C, wherein the second connector 14 of the first arm segment A of the plurality of arm segments 10 is engaged with the first connector 12 of the second arm segment B in a ball and socket engagement such that the second electrical contact(s) 17 of the first arm segment A are electrically connected with the second electrical contact(s) 18 of the second arm segment B, and the second connector 14 of the second arm segment B is engaged with the first connector 12 of the third arm segment C in a ball and socket engagement such that the first electrical contact(s) 18 of the third arm segment C are electrically connected with the second electrical contact(s) 17 of the second arm segment B. In this way, signals can pass from the first arm segment A to the third arm segment C.

Preferably, each arm segment 10 of the plurality of arm segments 10 is identical. However, the chain of identical arm segments 10 may be connected to one or more different components. For example, an end effector, sensor array (for example, lidar devices, Geiger counters, magnetic sensors, etc.), or camera assembly may be attached to the final arm segment 10 of the plurality.

As can be seen in the schematic representation of Figure 1 1 , each arm segment 10 of the plurality of arm segments 10 of a robot arm 1000, 3000 includes electronics 80, which may comprise one or more of a controller 82, energy storage device 84, wireless communication means 86, and/or sensor(s) 88.

Each set of actuators 20, 320 may be electrically connected to either of the two arm segments 10 to which it is physically attached. The arm segment 10 may comprise (for example, within the ball of the male connector 12) a controller 82 for controlling the set of actuators 20, 320 associated with the first connector 12 and/or the second connector 14 of that arm segment 10. Preferably, the controller is arranged to control the set of actuators 20, 320 associated with one of the first connector 12 or the second connector 14 of that arm segment 10. In this way, in a robot arm 1000, 3000 comprising a plurality of arm segments 10, each joint 100 will be controlled by a controller of one of the neighbouring arm segments 10.

The controller 82 may act as a slave to one nominated controller 82 among a plurality of interconnected arm segments 10. In this way, a chain of arm segments 10 may have a single controller 82 that controls all actuators 20, 320 for the robot 1000. Preferably, in that case, all of the controllers 82 will communicate via the electrical connector(s) 17, 18.

The controllers 82 may be configured to automatically detect how many arm segments 10 have been connected together and to automatically nominate a single controller 82 to control the assembly of arm segments 10. The arm segments 10 may interconnect such that all controllers 82 are connected to a bus that extends along the chain of arm segments 10 (e.g., formed via the electrical contacts of each joint 100). For example, the connection between the arm segments 10 may be a Controller Area Network (CAN bus).

Each controller 82 may be arranged to control the arm segment 10 in which it is installed and may communicating with the controllers 82 of the other arm segments 10. In some embodiments it is not necessary to nominate a main controller 82. Each arm segment 10 may carry one or more energy storage devices 84 (e.g. batteries or capacitors) for providing power to that that arm segment 10 (in particular, to the set of actuators 20, 320 associated with that arm segment 10). The energy storage devices 84 may be of a chain of arm segments 10 may be interconnected via the controllers 82 such that in the event of a failure of an energy storage device 84, power for that arm segment 10 may be supplied from one or more of the other energy storage devices in the chain of arm segments 10.

In some embodiments, the bus will provide communication between controllers 82, but not provide the power for each arm segment 10, i.e., it will be a communications bus. In such cases, each arm segment 10 may comprise a switched mode power supply unit that is connected to the energy storage device 84 of that arm segment 10 and to a power bus that extends along the chain of arm segments 10 (e.g., formed via a different set of electrical contacts of each joint 100).

The controllers 82 may be arranged such that each arm segment 10 controls its own power consumption from its own energy storage device 84 and from the power bus. This can allow power consumption of each set of actuators 20 to be independent from the voltage or current on the power bus.

Each arm segment 10 may carry one or more wireless communication devices 86 (e.g., WiFi, Bluetooth, ULF, etc.) for enabling the controller 82 of that arm segment 10 to communicate with external devices. Such an embodiment is preferred if the robot arm is to be autonomously powered. Wireless communication can be used to control devices attached to the robot arm 1000 that are not compatible with the communication bus described above. It is also possible for each arm segment 10 to be controlled

independently by the controller 82 of that arm segment 10, which may in turn be remotely controlled via the wireless communications device 86 of that arm segment 10.

Each arm segment 10 may carry one or more sensors 88 connected to the controller of that arm segment 10. The sensors 88 may including one or more of: a power monitor, an orientation sensor, a relative orientation sensor, etc.

The disclosed robot arm 1000 may also include positioning devices (such as optical emitters and/or sensors, magnetic emitters and/or sensors, and/or ultrasonic emitters and/or sensors) installed in the first and second connectors 12, 14 to enable a robot arm 1000 formed of a chain of arm segments 10 to align the last arm segment 10 of the chain with an unattached arm segment 10 for attachment therewith.

For example, in a ball and socket joint of the type set out above, the ball of a first arm segment 10 may have an emitter and/or sensor at the point lying on the longitudinal axis X, while the socket of a second arm segment 10 may have the other of an emitter and/or sensor at the point lying on the longitudinal axis Y. The emitter and sensor pair may be used to align the first and second arm segments 10. As mentioned above, in any embodiment of the joint 100, 200 set out above, there may be an end cap 16 that prevents detachment of the first connector 12 from the second connector 14. The end cap 16 has an aperture with a diameter less than the width of the first connector 12. The end cap 16 may be detachable from the second connector 14. For example, the second connector 14 may be provided with retaining device such as a threaded surface or a bayonet fitting) arranged to mate with a complementary retaining device (threaded surface or bayonet receiver) on the end cap 16. For example, a retaining thread may form the radially outermost surface of a cylindrical part of the second connector 14. In such an embodiment, the end cap preferably surrounds the arm segment 10 and rests upon the first connector 12. In the preferred example, it may be arranged to rest upon the ball of the ball and socket joint.

In some embodiments, it may be held in contact with the ball, but free to slide over the surface of the ball to enable rotation of the first arm segment relative to the second.

Most preferably, one of the retaining devices (e.g., a threaded surface or a bayonet fitting) of the end cap 16 or second connector 14 (preferably that of the second connector 14) may be driven to rotate by an actuator for effecting the retention. In this way, a robot arm comprising a chain of arm segments 10 may be actuated so as to engage a further arm segment 10 via the complementary retaining devices and automatically attach that arm segment 10 to the chain of arm segments 10 so as to form a longer chain of arm segments As described above, in all embodiments each joint 100 between arm segments 10 includes a first connector 12 of a first arm segment 10 and a second connector 14 of a second arm segment 10. The joint 100 enables relative rotation of the first and second arm segments 10 about more than one axis but maintains an electrical connection between the first electrical contact(s) 18 of the first arm segment 10 and the respective second electrical contact(s) 17 of the second arm segment 10.

Preferably, the first electrical contact(s) 18 are equally spaced around the longitudinal axis X of the male member 12, and the second electrical contact(s) 17 are equally spaced around the longitudinal axis Y of the female member 14.

In the embodiments described above, the connectivity is preferably maintained using the approach best shown in Figure 7. That is, the first electrical contacts 18 may be a set of conductive tracks 18 formed on an outer surface of the male member 12. Preferably, the conductive tracks 18 lie in grooves. The conductive tracks 18 are arc-shaped and lie in a spherical surface. The male member 12 and female member form a joint that allows rotation about the centroid of the spherical surface.

The second electrical contact(s) 17 may be a set of conductive wipers 17 (these could also be referred to as followers 17) defining an inner surface of the female member 14. The wipers 17 may each contact a respective one of the conductive tracks 18 to form electrical connections. Preferably, the wipers 17 extend into the grooves to thereby be held in alignment with the conductive tracks 18. It is preferred that the wipers 17 are sprung arms so as to be urged into contact with the conductive tracks 18. However, they may be a resiliently positioned conductive element of a different form.

The wipers 17 may be positioned such that in the longitudinal direction of the second arm portion 10 they are level with the centre of the sphere. In this way, irrespective of the relative orientations of the arm members 10, the wipers 17 can maintain contact with the tracks 18.

Alternatively, or in addition, the wipers 17 may be resilient to enable them to flex relative to the remainder of the female element 10, but to urge them towards respective equilibrium positions. This may enable them to move around the longitudinal axis Y of the second arm member 10 should this be necessary owing to manufacturing tolerances.

Whilst above, the second electrical contacts 17 are wipers and the first electrical contacts 18 are tracks, the same function can be achieved using wipers as the first electrical contacts 17 and tracks as the second electrical contacts 17.

An alternative means for maintaining connectivity may be as those described in

WO2016/009365. In that case, the second electrical contact(s) 17 of each second arm segment 10 comprise a plurality of grooves in an inner surface of the second member 14, each groove having an electrically conductive track extending along its length. The first electrical contact(s) 18 of each arm segment 10 comprise a plurality of depressions in an outer surface of the male member 12, each depression having an electrical contact therein. An electrically conductive ball bearing or roller is provided in each depression such that it is disposed in each groove of the second member 14 so as to form a conductive path between the electrical contacts and the electrically conductive track extending along the grooves.

Whilst above, the first electrical contacts 18 comprise depressions that hold a ball bearing and the second electrical contacts by 17 comprise a conductive track, the same function can be achieved by forming the second electrical contacts 17 with depressions holding ball bearings and the first electrical contacts 18 as conductive tracks.

Irrespective of the particular construction, in each type of connector described above, an electrical connection can be maintained by conduction between a conductor on the outer surface of the male member 12 and a conductor on the inner surface of the female member 14. The electrical connection is achieved either by direct contact between the first and second electrical contact(s) or by an intermediate conductive rolling element. Whereas in the embodiments described above, the actuators 20, 320 are provided outside of the joint, in other embodiments, the actuators 20, 320 may be provided inside the ball and socket joint.

Whereas in the embodiments set out above, each arm segment 10 may carry a male member 12 (e.g., a ball) at one end and a female member 14 (e.g., a socket) at the other end, it is also possible although less preferable, for there to be two types of repeating unit. One repeating unit may have a male member at each end, whilst the other would have a female member at each end. Preferably, the robot arm 1000, 3000 will include at least four arm segments 10.

The bail (or bail portion 12A) of the male member 12 may be generally spherical, in particular embodiments, as depicted in Figure 13, the ball portion 12A may comprise an engagement surface 122 which extends from at least a section of the ball portion 12A. The electrical connector has been omitted from this Figure for ease of reference, but a zenith direction may be defined passing through the centre of the ball portion 12A and the centre of the region where the electrical connector meets the ball portion 12A. The electrical connector may also define a zenith axis Z-Z which extends in the zenith direction. The electrical connector may be a discrete component which attaches to the bail portion 12A. Alternativeiy the electrical connector may be formed integral with the bail portion 12A. In either case, a centre may be defined in the region where this electrical connector meets the ball portion 12A. The engagement surface 122 is shaped to co-operate with a corresponding receiving surface on the socket portion 14A of the female member 14 in order to prevent the bail portion 12A and the socket portion 14A from rotating relative to one another about the zenith axis. The engagement surface 122 may be generally polygonal in planes orthogonal to the zenith direction. That is, the engagement surface 122 may comprise a plurality of faces 122A azimuthaliy spaced around the ball portion 12A (i.e. around the zenith axis). Each face 122A defines a non-contiguous (i.e. distinct) surface. In cross-sections orthogonal to the zenith axis the ball portion 12A is non-circular may form an N-sided polygon. Each face 122A may generally have the same radius of curvature (e.g. the same radius of curvature in a plane passing through the zenith axis). Each face 122A may have generally the same radius of curvature as any more strictly spherical parts of the ball portion 12A. Alternatively, different faces 122A may be provided with different radii of curvature to restrict movement of the bail portion 12A in the socket portion 14A. The current Figures show regularly repeating generally identical faces 122A. However, it is envisaged that the faces 122A may be irregular, in particular, there may be a single face 122A deviating from the strictly spherical shape, while the remainder of the ball portion 12A is generally strictly spherical. Irregular faces 122A in this manner can be used to ensure that the ball portion 12A can only be inserted in a particular orientation into the socket portion 14A. This can ensure that the same electrical contacts 17 are received in the same groove 124 every time the ball portion 12A and the socket portion 14A are made-up.

The engagement surface 122 may comprise grooves 124. Each face 122A may have a corresponding groove 124 provided thereon. Alternatively, there may be some faces 122A without a groove 124 thereon. The groove 124 may be generally provided in the centre of the face 122A. The groove 124 may be longer than the face 122A in the polar direction.

There may be any number of faces 122A, but in preferred embodiments there may be eight faces 122A (referred to as an octo-bail). When viewed from above as in Figure 15, the outer perimeter of the octo-bail is generally octagonal. The ball portion 12A preferably has at least eight faces 122A, which can allow the ball portion 12A to have a smooth movement across its entire range of movement while still preventing the relative rotation about the zenith axis.

The engagement surface 122 may extend over a middle part of the ball portion 12A (with respect to the zenith direction). The top 125 and bottom 127 of the ball portion 12A may be more strictly spherical. The top section 125 or bottom section 127 may include the attachment point for an electrical connection across the joint, as shown in Figure 14. Figure 13 shows an alternative to the ball portion 12A of Figure 13. This alternative has a less pronounced engagement surface 122 compared to Figure 13. Each groove 124 is generally on a more strictly spherical path, with protrusions 122B formed on the ball portion 12A to form the polygonal shape. This can be best seen on Figure 16 which is a side view of the bail portion 12A of Figure 14 and on Figure 17 which is a cross-sectional view along V-V from Figure 15. For clarity, some of the internal detail of the ball portion 12A has been omitted from the cross-sectional view of Figure 17.

The bail portion 12A may be formed of first and second bail sub-assemblies 12B, 12C. These sub-assemblies 12B, 12C may be generally hemispherical and connect together to form the ball portion 12A, For example, the sub-assemblies 12B, 12C may have a snap-fit connection.

The receiving surface on the socket portion 14A is correspondingly shaped in order to prevent the ball portion 12A from rotating about the zenith axis. As such, the major degrees of freedom of the ball portion 12A are maintained, while preventing relative rotation in this direction which could otherwise potentially act to unseat the connection across the joint.

Figure 14A shows a socket portion 14A arrange to co-operate with the ball of Figure 14. The socket portion 14A has a plurality of receiving faces 122C which are shaped to correspond to the faces 122A of the ball portion 12A. As can be seen in Figure 15A which shows Figure 14A from above, the receiving faces 122C generally form a corresponding polygonal shape (in this case an octagon). The receiving faces 122C increase in width the deeper into the socket portion 14A they extend. This is to ensure that the movement of the extrusions 122B of the bail portion 12A is accommodated across the entire range of movement of the ball portion 12A. The increase in width the extrusions 122B of the bail portion 12A can allow a more pronounced (less spherical) shape of the ball portion 12A without the risk of it jamming against the receiving faces 122C and inhibiting other motion of the bail portion 12A than is intended.

Electrical contacts 17 are provide in the socket portion 14A to contact the grooves 124 of the ball portion 12A. The electrical contacts 17 are provided in a notch 122D formed in the receiving faces 122C. The electrical contacts 17 are free to flex in this notch 122D to ensure the ball portion 12A can travel across its entire range of movement.

Figures 14B and 15B show the ball portion 12A and socket portion 14A connected together, in this connected position the electrical contacts 17 fit in the slots 124 of the ball portion 12A. The bail portion 12A and socket portion 14A are able to move relative to each other in conventional bail and socket directions, but are restricted from rotating relative to one another about the zenith axis Z-Z (shown in Figure 14B).

While the Figures all show the grooves 124 on the ball portion 12A and the electrical contacts 17 on the socket portion 14A, embodiments are considered in which the opposite is the case. Any of the ball portions 12A and socket portions 14A disclosed and described above with respect to Figures 13 to 17 may be used in any of the joint embodiment previously described,