HK1069355B - Robot arm - Google Patents

Description

Mechanical arm

Technical Field

The present invention relates to a robot arm.

Background

In the conventional art, mechanical equipment such as an engine and a machine including a casing is maintained on a regular maintenance schedule. In the event of a fault, an operator or engineer will run the machine or engine through a series of functional tests in accordance with a troubleshooting program and record the response of the machine or engine to each test function. From observing the reaction or reaction of the machine to a given test function, an approximate region of machine failure can be diagnosed, at least in part. Thereafter, the machine is disassembled to some extent to enable possible faults to be identified and repairs to be carried out.

Our co-pending uk patent application No.0020461.0 (the disclosure of which is incorporated herein by reference) describes and proposes an apparatus comprising a working head adapted to carry a tool or inspection element for performing work or inspection at a location within a machine, the apparatus comprising a support arm for the working head, the arm being adapted to be advanced into the machine to position the working head in a position for operation, operating means for operational control of the working head, and control means for controlling the attitude and positioning of the arm within the machine, wherein the support arm comprises at least one segment having a plurality of links, each link encircling its adjacent link, and means for controlling the position and/or attitude of the segment in dependence on data, thereby enabling the arm to follow and adapt to a predetermined path within the machine, from the inlet of the machine housing to the site of operation.

In a particular aspect of the invention described in this application, each segment comprises a plurality of links, with a degree of circumferential articulation between adjacent links. By maintaining the articulating joints of the links in each segment under tension, the spatial positioning of each segment can be precisely controlled so that the arm can follow a convoluted path to guide the work tool into the machine. Arms of this type are sometimes referred to as "snake", "serpentine" or serpentine arms because of their ability to follow a convoluted path extending in a serpentine manner along their own axis and flowing around an obstruction.

The invention described in uk patent application No.0020461.0 requires careful design of the components to minimise frictional losses at the loop joints between each pair of connectors. In a multi-link segment, these frictional losses build up and therefore, in a multi-segment manipulator arm, the total frictional losses that must be overcome during manipulation of the arm can be quite large. Therefore, there is a need for a device in which the components are relatively straightforward to manufacture and in which frictional losses are reduced. In the arrangement particularly described in uk patent application No.0020461.0, spring means may be provided to bias the respective connectors against the compressive tension applied by the control cable.

Disclosure of Invention

The applicant has found that by arranging the springs and instead inserting a layer of rubber or elastomeric material, or bonding or keying to the two elements forming the loop between adjacent connectors within a segment, the effect of the spring is that the spring is not constrained to move relative to the segments. The rubber provides a fixed frictional contact between the articulating components while at the same time providing the resilient shear necessary to produce joint "stiffness".

Thus, according to one aspect of the present invention, there is provided a robotic arm comprising a plurality of segments, each segment comprising a plurality of links, each link comprising: first and second coupling members each adapted for limited movement one with respect to the other, and elastomeric means disposed between said first and second coupling members, wherein the first and second coupling members are configured in cooperative mating relationship with the elastomeric means disposed therebetween, the elastomeric means being keyed or bonded to the first and second coupling members, whereby bending movement between the coupling members produces shear movement within the elastomeric means, reducing any compression movement due to relative movement between said first and said second coupling members.

The elastomer may be natural rubber or synthetic rubber, or any other suitable elastic or elastomeric material. The elastomer is preferably arranged as a sandwich between said first and second connection elements. In another embodiment of the invention, the first and second coupling elements may be configured in cooperative mating relationship with each other and the elastomeric means may be disposed therebetween as a thin layer, whereby a bending movement between the coupling members creates a shearing movement within the elastomeric means that minimizes any compression movement as a result of the relative movement between said first and said second coupling elements. The elastomer may act to create axial stiffness and bending flexibility of the joint between the two connecting elements.

Preferably, the thickness of the layer is as thin as possible, with a layer thickness of 1mm or less being preferred. The layer may be bonded to one or both of the connecting elements or may be bonded to one or both of the connecting elements. The surfaces adjacent the connecting elements are preferably fixed in operation so that relative movement between the connecting elements produces a shearing motion within the elastomer. The thickness of the layers will reduce the tendency to compress and therefore provide improved stability of the locating features and increase the axial stiffness of the connector loops in the segments.

Elastomeric devices may include multiple elastomeric layers, where a rigid layer bonded or bonded to an adjacent elastomeric layer may be used to separate each elastomeric layer from its adjacent layers. The elastomeric means may be laminated, the layers may be crossed or the rigid layers may be any rigid layer, or material that can be bonded or bonded to the elastomer. The cross-ply should be sufficiently rigid to minimize compression movement of the elastomer. Typical materials for the cross layers may be thin metal layers, resin or glass fibres, or may be woven or non-woven carbon fibre or Kevlar mats.

The invention also includes a robotic arm comprising at least one segment comprising a plurality of links according to the invention, and control means for controlling the movement of said links within the segment, wherein the control means maintains said links in a tensioned or compressed state. The control means may be at least one wire extending from one end of the segment to the other.

In a preferred aspect of the invention, the control means may comprise three wires, each extending from one end of the segment to the other, whereby varying the tension in the wires relative to one another causes or allows the connector to flex, thereby controlling the movement of the segment. The wire is preferably tensioned to maintain the connector in a compressed state. The application of differential tension between the wires causes or allows the segment to move or bend.

In a preferred embodiment of the invention, each connector may be formed from three parts,

an outer disc preferably has holes for the control wires so that the control wires preferably extend outside the other parts of the connector.

An inner circular disc adapted to be arranged substantially inside the outer circular disc and having a central bore for receiving control means and/or power supply means for the working head, and

an elastomeric disc or layer extending between the respective inner and outer discs which is bonded or keyed to the respective disc but which otherwise floats freely between the inner and outer discs so that the inner disc is free of the other components of the assembly.

A robot arm may comprise a plurality of segments according to the invention, wherein each segment is provided with control means. At least one of the rods of each connection may be provided with means for guiding the wire from one end of the segment to the other. The wire may be disposed outside of the segment connectors. Each wire may terminate in a ferrule adapted to engage a corresponding recess in the end cap of a segment to tension the wire, the ferrule engaging the end cap to apply a compressive load to each segment to maintain the rigidity of the connection within the segment.

Each control line may be operated by an actuator: where there are control wires for multiple segments, the actuators are spaced in one or more arcs around one actuator plate or the head plate adjacent one end of the first segment. Typically the actuator array may provide one actuator for each wire which may be arranged in spaced arcuate relationship to form a truncated cone. The wire from each actuator may be passed around a guide such as a pulley to provide a straight lead-out for the control wire.

In another aspect of the invention, at least some of the actuators may be located within the segment assembly, in which case means for actuating the actuators is necessary. Such means may comprise a data connection cable, or a wireless data transmission means of the type generally known in the art. In the latter case, the use environment must be considered in order to determine the best means of control.

A segment may be formed stepwise from a series of connections, or the completed segment may be assembled in a form and injected with elastomer into the void between the components in the form of a mould tool. In this way, complete segments of the connection can be formed rather easily and quickly.

In another embodiment of the invention, each connector may be formed from a pair of half-links, which may then be assembled back-to-back. Thus, an inner half joint and an outer half joint can be assembled with their joint rubber layers. The connector halves can then be assembled back-to-back or front-to-front to form an integral connector component, with the components together forming a segment.

The applicant has found that the semi-joined parts can be formed in three separate individual parts, namely an outer joint part, an inner joint part, and a rubber bearing. It is desirable that the bearings be keyed to each of the coupling components to allow one component to move relative to the other to create a shearing motion or force within the rubber component. The different half-links can then be "pinned" together by means of dowel pins disposed in matching holes on the respective components. The assembly can be made "loose" and the cables can be threaded through various access holes in the outer attachment perimeter attached to the actuator or head plate. Alternatively, the components may be fixedly joined together with glue. Once the actuator reacts to create a degree of tension in the plate, all of the components are held together so that by varying the tension in the wire, the segment can be caused to bend appropriately. The first and second connecting elements, or parts of the connection, which constitute each connecting part, may form a rubber part in between, or be a spherical or conical shell, or an intermediate between a spherical or conical, or even be annular. If the parts are spherical, all deformation of the spherical parts is effected by shearing as the inner disc rotates relative to the outer disc. If the design of the member is changed so that it is no longer spherical, rotation of one part relative to the other causes the elastomer to exercise its bulk modulus, i.e., the shear member; there is a resultant localized tension and compression parallel to the axis of the connection. This makes any non-spherical joint stiffer than a spherical joint of roughly equivalent basic dimensions.

Replacing each connected rubber part with a plurality of layers, as described above, in order to introduce more than two thinner metal sheets, has significant advantages. This allows such a link to have a greater range of motion more effectively than simply doubling the number of links per segment. The length added to a connector by doubling the bend angle is less than doubling the original connection pitch. This idea can be extended within reasonable limits. The thin, rigid shell between the two rubber layers serves to constrain the rubber sections so that the two rubber sections provide about the same shear stiffness as a single rubber section of double thickness, but the two rubber sections of smaller thickness are stiffer than the single section of double thickness.

In this particular embodiment, if two adjacent connectors are bent such that the outer peripheries meet, the diametrically opposed positions move apart, thus acting to define an annular segment. In these cases, the inner disc is free to move relative to the outer disc. The purpose of this design is that the centre of rotation of the holding part is stationary and in a position at the centre of the spherical surface of the inner disc in the undeformed position. Essentially, this situation is similar to a ball and socket joint, where there is no friction but only viscous losses in the rubber and a small amount of axial compression applied to maintain the stiffness of the joint.

By using elastomeric discs or bearings between the moving parts of the respective links, friction is significantly reduced, while the device becomes extremely easy to mass produce. Once the tools and templates have been made, mass replication becomes considerably easier. Segments consisting of a large number of links can be formed and the preferred control for each segment is 3 wires. Although it is possible to configure one wire within a segment, or at least one operating wire within a segment, it is preferred to use at least 3 control wires in order to obtain an optimized manipulation of the segment. For a multi-segmented robotic arm, three sets of control wires would be required for each, so that eight segmented arms would require a total of 24 control wires, each with a separate actuator control.

In another aspect of the invention, an outer sleeve may be provided around each segment, and in a particular embodiment of the invention, the sleeve may be a bellows-type shell. The use of such a housing has numerous advantages in that it increases the torsional/bending stiffness of the connector. This is particularly advantageous as it can increase the torsional stiffness of the arm with very little bending stiffness using a suitable construction of the bellows housing.

Another benefit of the housing is that it protects the wires and other components from external damage and enables the entire segment to be filled with lubricant. Typical lubricants may be dry powders or liquids such as greases and/or oils. The physical properties of the lubricant contained within the arm may be selected according to the environment in which the robotic arm is to operate. A particular feature of this embodiment of the invention is that as the arms flex, the geometry of the gaps between adjacent links changes, which has the effect of displacing or "pumping" lubricant from one region of the segments to another, and ensures effective lubrication of the components due to the circulation of lubricant within each segment. In another aspect of this particular feature of the invention, the arm may be provided with a lubricant reservoir through which lubricant may be continuously pumped and recirculated back to the lubricant reservoir. This embodiment is particularly useful where the arm is used in aggressive environments and where the arm requires cooling. In this case, the cooling device may comprise a lubricant tank.

The paths may be formed using the apparatus according to the present invention by using a joystick control assembly for click guidance, or by providing off-line or on-line techniques to computer control through a CAD model of the proposed environment.

Drawings

The following is a description with reference to the drawings of an embodiment of the device according to the invention.

In the drawings:

fig. 1 is a perspective view of a plurality of connectors in a segment according to the present invention.

Fig. 2 is an exploded schematic view of the "half" connector of fig. 1.

FIG. 3 is an end view of the "half" connector of FIGS. 1 and 2; and figure 3A is a cross-sectional view on line a-a of figure 3.

FIG. 4 is a perspective view of an end cap showing the connection assembly of the ferrule at the distal end of a segment.

Fig. 5 is a sectional view on line a-a of fig. 6.

Fig. 6 is an end view of another embodiment of the present invention.

Fig. 7 is an exploded view of the "half" connector in the embodiment of fig. 5 and 6.

Fig. 8 is a head plate showing a three actuator configuration for a single segment.

FIG. 9 is a frustoconical configuration for multiple actuators to control a control line for a robotic arm having multiple segments.

Fig. 10 is a perspective view of a segment of a sheath for an arm according to the present invention.

Detailed Description

A robotic arm according to the invention comprises a plurality of segments 10 arranged end-to-end to form an extended "serpentine" arm. Each segment comprises a plurality of connectors 11. Each connection element 11 comprises a first connection element 12 and a second connection element and thread guide 13. The first connecting member is the inner disc 12 and the second connecting member is an outer disc. The inner disc 12 is shaped to provide an arcuate annular surface 14 and the outer disc 13 has a matching arcuate surface 15.

Assembled as shown in figure 1, the inner disc 12 and outer disc 13 are separated by a rubber layer 16 which may be formed in situ. The rubber layer 16 is bonded to each of the outer disc 13 and the inner disc 12 to allow relative movement therebetween. Each inner disc is provided with a central bore 17 to form a central cavity through the centre of the device for receiving power and control means for the working head at the end of the arm. Each connector 11 may be formed of a pair of "half-links", which are most clearly shown in figure 2. Each half-joint comprises an outer joint member 13, an inner joint member 12, and a rubber disc or shell 16 adapted to be inserted between the two. The components may be bonded together to form one half of the connection and then joined together with adjacent components to form a continuous connector termination. It should be noted that the arcuate surface 15 of the outer connecting member 13 is adapted to cooperate with the lower surface of the corresponding element 12 (as shown in figure 2). The disc 16 is shaped to be received therebetween and the parts may be bonded together. This can be clearly seen in fig. 3A, which shows a cross section through the adhesive part.

In one aspect of the invention, the outer disc and wire guide 13 is provided with a plurality of circumferentially spaced pin holes 23, while the inner disc 12 is also provided with corresponding diametrically spaced pin holes 24. When the components are placed together with pins located in holes 23 and 24, respectively, those skilled in the art will recognize that a permanent fixation would not be necessary if the components were held in tension by control wires. The outer disc 13 is provided with a plurality of through holes 25 adapted to form wire guide holes to accommodate the control wires of the device.

Thus, the half link members can be positioned by means of locating pins disposed in mating holes on each assembled half link member, whereby the assembly can be formed without further connection between the half link members, and the cables can be threaded through various operating holes on the outer connecting periphery attached to the actuator plate, the arrangement being such that actuation of the actuator produces a degree of tension in the plate and in the cables, whereby the entire assembly is held together so that the segment can be properly manipulated by varying the tension in the wires.

Each segment may be provided with an end cap 30 (see figure 4) provided with circumferentially spaced wire receiving holes and an enlarged recess 26 (the wire receiving holes and recess constituting control wire anchoring means for securing the segments) comprising a ferrule 27 attached to the end of a control wire 28. During assembly of the device, the end cap 30 is secured to the adjacent outer disc portion 13 of the end connector and the control wire 28 is threaded through a suitable recess 26 in the end cap 30 and then through a matching hole 25 in each outer disc portion 13 of the connector in each segment.

Several segments are then joined together end-to-end to create a mechanical arm of suitable length for the application. This "snake-like" mechanical arm has the ability to be manipulated to flow axially along its length and follow a convoluted path in a snake-like manner.

The end of the wire is returned to the actuator and tensioned until the ferrule 27 abuts against the back plate to hold the assembly in tension. In this manner the assembly is tensioned and the connection of the parts as shown in figures 5, 6 and 7 is avoided and the mating surfaces of the inner and outer discs are suitably grooved to receive a correspondingly shaped rubber disc 16. These grooves or profiles serve to key the disc 16 at a location between the inner and outer discs 12 and 13 respectively and allow movement of one relative to the other in response to changes in tension in the control wire 28. This may eliminate the need for disk connections and allow for easy replacement of damaged components within any given segment.

In the assembled segment, the outer surface of the disc and the control wire may be sealed and the resultant cavity and wire guide filled with a lubricant so that the control wire moves in a lubricated environment. This in turn serves to reduce losses and friction during use.

Each control wire is operated by an actuator, wherein the actuator associated with each control wire is spaced in one or more arcs around the head plate adjacent one end of the first segment. The actuator array provides an actuator for each of the wires which may be arranged in spaced arcuate relationship to form a truncated cone, and further the wires leading from each actuator are passed around a guide or pulley to provide a lead-out for the control wires from the actuator to the entrance into the segment.

Adjusting the tension on the wires controls the operation of the segments. Figure 8 shows a simplified three actuator control panel comprising a base plate member 40 having at its end facing the base plate an upstanding mounting plate assembly 41 adapted to mount the end plate of a segment 42. The control wires 28 extend through the mounting plate assembly 41 to the operating tubes 43 of the respective actuators 44. The central actuator 44 provides a direct feed of the wire 28 from the segment to the actuator itself, while the actuators on either side of the central actuator reduce any friction or wear in operation to a minimum by means of a pulley arrangement 45.

Each actuator 44 may be controlled manually or by a computer to vary the tension in the three wires 28. Depending on the tension change, each individual link seeks to move in response to the change in tension in the wire, thereby creating motion in the segment to allow the end of the guide segment to be guided to a given location in the work place.

Of course, more actuators may be required for multiple segments in an extended "snake" arm, typically three per segment. In these cases, the actuator must be constructed to provide access to the control line at the exit from the end of the first segment in a relatively small space. Thus, the actuators may be arranged in an arc such that the control line or conduit containing the control line for each actuator forms a cone rather as shown in figure 9.

The rubber disc 16 may be a single piece of rubber or may be in the form of an elastomer in a composite rigid layer, the applicant has found that the thinner the thickness of the single rubber layer, the more effective the final layer and the stiffer the connection between the inner disc and the corresponding outer disc. The rigid layer between the elastomer layers is a material that can be bonded or bonded to the elastomer. The rigid layer is sufficiently rigid to minimize compression of the elastomer during movement of the connection. The rigid layer may comprise a thin metal layer, a resin or fiberglass layer, or may be a mat of woven or non-woven material.

The device according to the invention also provides a sealing of the bearing surface between the inner and outer discs to prevent the ingress of harmful material from the atmosphere (see figure 10). In addition, the central bore or cavity 17 effectively seals and provides access for power and control means for the working head at the end of the robot arm.

The sealing may be effected by the casing 100 being provided with circumferential corrugations 101. The housing 100 extends outside the outer surface of each outer disc and the wire guide 13. The housing 100 seals the space between each outer disc and the wire guide 13 and is filled with oil or other lubricant, thereby allowing the control wire to operate in a lubricant environment. Suitable lubricants are oils, powders and greases, the viscosity and other physical properties of which will be selected according to the environment in which the arm is to be used.

The use of the housing 100 having a corrugated structure has the effect of increasing the torsional and/or bending stiffness of the connectors relative to each other. This can result in the arm significantly increasing the arm torsional stiffness with very little increase in bending stiffness. This structure serves as a reason for protecting the wires and other components from external damage.

The containment of lubricant by the housing 100 has major advantages in operation. As described above, as the segments flex, the adjacent peripheral edges of the outer disc and the wire guide 13 move closer together, while diametrically opposed portions of the same disc 13 move apart. As a result, the lubricant-containing chamber changes shape from an annular cavity of substantially continuous and substantially uniform cross-section to a "wedge" shape. This causes lubricant to move from the inner or "narrow" side of the wedge and be effectively pumped onto the "wide" side of the wedge on the outside of the arc. In this way, the lubricant passes through the individual threads. Thus, this pumping effect serves to provide effective lubrication of the components within the arm, particularly the wires, each time the segment is bent, or each time the plane of curvature changes.

The arm may be provided with a lubricant reservoir and a means for pumping lubricant through the arm and recycling it back to the reservoir. When the arm is used in an aggressive environment, a lubricant cooling device is provided to cool the arm.

It should be appreciated that the lubricant may be introduced into the mechanical arm in a number of different ways. In one embodiment of the invention, the chamber may be filled with lubricant at the time of assembly and effectively sealed over a long period of time. In another embodiment of the invention, the individual connections or segments of the arm may be isolated and lubricant introduced through a point of passage such as a grease nipple, with excess lubricant being released through an additional port or pressure relief valve. In another aspect of the invention, the entire arm may be integrally lubricated by passing lubricant along the entire length of the arm using the wire holes in the outer connecting member. The liquid lubricant may be continuously pumped through the arms and recirculated back to the central sump. Such a configuration would allow temperature control of the lubricant within the arm by heating or cooling the lubricant, and the present invention includes providing a temperature control device for the liquid contained within the arm.

Claims (33)

1. A robotic arm comprising a plurality of links, each link comprising: first and second coupling members each adapted for limited movement one with respect to the other, and elastomeric means disposed between said first and second coupling members, wherein the first and second coupling members are configured in cooperative mating relationship with the elastomeric means disposed therebetween, the elastomeric means being keyed or bonded to the first and second coupling members, whereby bending movement between the coupling members produces shear movement within the elastomeric means, reducing any compression movement due to relative movement between said first and said second coupling members.

2. A robotic arm as claimed in claim 1, in which the elastomeric means is natural or synthetic rubber.

3. A robotic arm as claimed in any one of the preceding claims, in which the elastomer means is provided as an elastomer layer between the first and second coupling members.

4. A robotic arm as claimed in claim 3, in which the thickness of the elastomeric layer is 3mm or less than 3 mm.

5. A robotic arm as claimed in claim 3, in which the elastomeric layer may be bonded and/or keyed to one or both of the coupling elements.

6. A robotic arm as claimed in claim 5 in which the surfaces of the elastomeric layer adjacent the link elements are effectively anchored so that relative movement between the link elements in operation produces a shearing motion in the elastomeric layer, the arrangement being such that the thickness of the elastomeric layer has a reduced tendency to compress, thereby providing improved stability of the positioned part.

7. A robotic arm as claimed in claim 3, in which the elastomeric means comprises a plurality of elastomeric layers.

8. A robotic arm as claimed in claim 7, in which a rigid layer is bonded or keyed to adjacent elastomer layers to separate an elastomer layer from its adjacent elastomer layer.

9. A robotic arm as claimed in claim 7 or 8, in which the elastomeric means is laminated.

10. A robotic arm as claimed in claim 8, in which the rigid layer between the elastomer layers is of a material which is bondable or keyed to the elastomer layers.

11. A robotic arm as claimed in claim 10, in which the rigid layer is sufficiently rigid to minimise compression of the elastomeric layer during movement of the link member.

12. A robotic arm as claimed in claim 8, in which the rigid layer comprises a thin metal layer, a resin or fibreglass layer, or a mat of woven or non-woven material.

13. A robotic arm as claimed in claim 12, in which the woven or non-woven material is carbon fibre or Kevlar.

14. A robotic arm as claimed in claim 1 wherein a plurality of links form a segment and control means are provided for controlling the movement of said links within the segment, wherein the control means maintains said links in tension or compression.

15. A robotic arm as claimed in claim 14, in which the control means comprises at least one wire extending from one end of the segment to the other.

16. A robotic arm as claimed in claim 14 wherein the control means comprises three wires each extending from one end of the segment to the other, whereby varying the tension in the wires relative to one another causes or allows the links to flex, thereby controlling the movement of the segment.

17. A robotic arm as claimed in claim 15 or 16, in which the wire is tensioned to maintain the links in compression.

18. A robotic arm as claimed in claim 15 or 16, in which the second coupling member is an outer disc having apertures for control wires such that the control wires extend substantially externally of the coupling member, the first coupling member is an inner disc adapted to be disposed substantially internally of the outer disc and having a central bore to receive control means and/or power supply means for the working head, and a rubber disc or layer extends between the respective inner and outer discs, the rubber disc or layer being bonded or keyed to the respective disc but being free to float between the inner and outer discs.

19. A robotic arm as claimed in claim 14, comprising a plurality of segments, wherein control means are provided for each segment.

20. A robotic arm as claimed in claim 19 wherein each segment terminates in an end cap having wire conduit means for the control wires of the segment of the arm, and anchoring means arcuately spaced around the end cap for securing the control wires of the segment.

21. A robotic arm as claimed in claim 15, in which at least one of the link elements of each link is provided with means for guiding a wire from one end of the segment to the other.

22. A robotic arm as claimed in claim 15 wherein the wires are disposed externally of the segment links and terminate in a ferrule adapted to engage a corresponding recess in an end cap of a segment to tension the wires, the ferrule engaging the end cap to apply a compressive load to each link to maintain the stiffness of the links in the segment.

23. A robotic arm as claimed in claim 15 in which each control wire is operated by an actuator, wherein the actuator associated with each control wire is spaced in one or more arcs around the head plate adjacent one end of the first segment.

24. A robotic arm as claimed in claim 23 wherein the actuator array provides an actuator for each wire which may be arranged in spaced arcuate relationship to form a truncated cone and further wherein the wire leading from each actuator passes around a guide or pulley to provide a lead-out for the control wire from the actuator to the entrance to the segment.

25. A robotic arm as claimed in claim 1, in which each link is formed from a pair of link halves which are assembled back to back.

26. A robotic arm as claimed in claim 25 wherein each half link comprises three separate and separate parts, a first link element, a second link element and elastomeric means, wherein the elastomeric means is bonded or bonded to each link element to cause movement of one element relative to the other to generate a shearing motion or force within the elastomeric means.

27. A robotic arm as claimed in claim 26 wherein each half link is positionable by means of locating pins located in mating holes in each assembled half link whereby the assembly may be formed without further connection between the half links and the cables may be threaded through various operating holes in the outer connecting periphery attached to the actuator plate, the arrangement being such that actuation of the actuator generates a degree of tension in the plate and in the cables whereby the entire assembly is held together so that the segment may be manipulated appropriately by varying the tension in the wires.

28. A robotic arm as claimed in claim 14, in which an outer sleeve is provided around each segment.

29. A robotic arm as claimed in claim 28, in which the sleeve is a bellows-type housing.

30. A robotic arm as claimed in claim 28, in which the enclosed segments of the housing are filled with a lubricant.

31. A robotic arm as claimed in claim 30, in which the lubricant may be a dry powder or a liquid, and in which the physical characteristics of the lubricant contained within the arm are selected in dependence on the environment in which the arm is to operate.

32. A robotic arm as claimed in claim 30 or 31, in which the arm is provided with a lubricant reservoir, and means for pumping lubricant through the arm and recycling it back to the reservoir.

33. A robotic arm as claimed in claim 32, in which lubricant cooling means are provided to cool the arm when the arm is used in an aggressive environment.