WO2014128493A1

WO2014128493A1 - Collaborating robots

Info

Publication number: WO2014128493A1
Application number: PCT/GB2014/050528
Authority: WO
Inventors: Colm Mckeown; Mark BOWERING
Original assignee: The University Of Bristol
Priority date: 2013-02-25
Filing date: 2014-02-21
Publication date: 2014-08-28
Also published as: GB201303255D0; GB201514821D0; GB2525549A

Abstract

The invention relates to robot cooperation where not only can the robots cooperate on a single task, the robots can actually physically connect to each other to perform a single operation.

Description

Collaborating robots

FIELD OF THE INVENTION

The present invention relates to a robot arrangement including a plurality of robots arms.

BACKGROUND OF THE INVENTION

Robot use is well known in industry for the automation of a variety of operations. An industrial robot typically includes a moveable arm with an end-effector at the distal end of the arm, designed to interact with the work environment. End-effectors can take a variety of forms, including tooling for e.g. drilling, spot welding, measuring, gripping, etc. The end-effector may be fixed to the robot arm for performing a particular operation, or may be replaceable so as to enhance the flexibility of the robot for performing a variety of different operations depending upon which end-effector is attached. A single end-effector may also include a plurality of tools, each for performing different operations.

Robots can be used individually, but are commonly used in groups with each robot being responsible for a particular operation in a task. Occasionally robots in robot groups are programmed to cooperate simultaneously on the same task, with one robot aiding or complementing the operation of another. For example, one robot may hold two work pieces together while another robot performs a drilling operation on them. A robot may also include a plurality of robot arms, the arms working individually or in cooperation as desired.

Since the robot arm is cantilevered off the base of the robot, there will be some inherent play in the robot arm leading to potential inaccuracy at the end-effector. Whilst great steps have been made in recent decades, with developments such as zero backlash motors, the drive for greater accuracy in demanding applications means that there is still room for improvement. In the example of a 6-axis jointed arm robot having a drill for an end-effector, this play affects the ability of the robot to hold the drill in a fixed position during a drilling operation, which in turn affects the accuracy of a hole being drilled. Furthermore, vibrations during drilling further aggravate the situation. In high-end manufacturing sectors such as the aviation industry, this is not acceptable. SUMMARY OF THE INVENTION

By having at least one other robot connected to the end-effector, e.g. a drill, of the first robot, the cantilever effect and the play in the robot structure can be significantly reduced. Depending on the number and position of the robots, these detrimental effects can be negated. For example, two robots located opposite each other and connected to the common end-effector would significantly reduce the cantilever effect. Three robots, if spaced approximately equidistant from the end-effector and spaced at equal angles from each other, would provide yet more stability. While more robots can be used, three is believed to be the optimal number providing maximum improvement in stability for the number of robots, the overall arrangement functioning in very much the same fashion as a tripod. Using more robots than one may also help reduce the effects of vibration. A first aspect of the invention provides a robot arrangement comprising: a plurality of robot arms each having a distal end; and at least one end-effector carrier attached or attachable to the distal end of at least one robot arm and configured to carry an end-effector for performing one or more operations in the environment of the robot arrangement, wherein the robot arrangement is operable in a first mode in which first and second robot arms of the plurality of robot arms are coupled together either: i) by coupling of their respective distal ends to only one end-effector carrier, or ii) by direct coupling together of end-effector carriers attached to the distal ends of the respective robot arms, such that the first and second robot arms are moveable in unison, and a second mode in which the first and second robot arms are decoupled from each other such that the first and second robot arms are moveable separately.

A second aspect of the invention provides an end-effector carrier for a robot arrangement, the end-effector carrier comprising: a first engagement interface configured for attachment to a distal end of a first robot arm; a second engagement interface configured for attachment to either a distal end of a second robot arm or to a second end-effector carrier; and either: i) an end-effector integral with the end-effector carrier, the end-effector being configured to perform at least one operation in the environment of the robot arrangement, or ii) an end-effector engagement interface for detachable attachment to an end- effector configured to perform at least one operation in the environment of the robot arrangement.

A third aspect of the invention provides a method of operating a robot arrangement, the method comprising: providing a plurality of robot arms each having a distal end; providing at least one end-effector carrier attached to the distal end of at least one robot arm and configured to carry an end-effector for performing one or more operations in the environment of the robot arrangement; operating the robot arrangement in a first mode by: coupling together first and second robot arms of the plurality of robot arms either: i) by coupling of their respective distal ends to only one end-effector carrier, or ii) by direct coupling together of end-effector carriers attached to the distal ends of the respective robot arms, and moving the first and second robot arms in unison, and operating the robot arrangement in a second mode in which the first and second robot arms are decoupled from each other, by moving the first and second robot arms separately. A fourth aspect of the invention provides a robot arrangement comprising: a plurality of robot arms each having a distal end; and a single end-effector carrier fixedly attached to the distal ends of the plurality of robot arms and configured to carry an end-effector for performing one or more operations in the environment of the robot arrangement, wherein the robot arrangement is operable such that the first and second robot arms are moveable in unison.

A fifth aspect of the invention provides a method of operating the robot arrangement according to the fourth aspect, the method comprising moving the robot arms in unison. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 illustrates a plan view of an exemplary robot arrangement of a first embodiment including three 6-axis jointed arm robots mounted on rails for performing separate operations in a robot zone (note: no end-effectors for performing the separate operations are shown attached to the robot arms); Figure 2 illustrates the three robots, with one of the robots having picked up an end- effector carrier (shown schematically) having a triangular shape;

Figure 3 illustrates the three robots all attached to the same end-effector carrier for performing a collaborative operation in the robot zone; Figure 4 illustrates in detail the end-effector carrier having three robot engagement interfaces for engaging the distal end of the arm of the respective robots in figure 3, and an end-effector (in this example, a drill) fixed to the end-effector carrier;

Figure 5 illustrates in detail a second example of the end-effector carrier similar to that shown in figure 4 but having a quick change end-effector engagement interface configured for attachment to one of a plurality of interchangeable end-effectors (not shown);

Figure 6 illustrates the three robots all attached to a third example of an end-effector carrier (shown schematically) having a pyramid shape;

Figure 7 illustrates the three robots all attached to a fourth example of an end-effector carrier (shown schematically) having a cube shape;

Figure 8 illustrates a second embodiment in which each of three robots has a respective end-effector carrier (shown schematically) for performing separate operations, and

Figure 9 illustrates the robots of the second embodiment joined together by their end- effector carriers for performing a collaborative operation using one of the end- effectors.

DETAILED DESCRIPTION OF EMBODIMENT(S)

Figure 1 shows a robot arrangement in accordance with a first embodiment which includes a plurality of robots - in this example three robots 1, 2, 3. The robots 1, 2, 3 are substantially identical. The robots are 6-axis jointed arm industrial robots, e.g. a 6-axis industrial robot from Kuka AG. Each robot comprises a base 4 slidably mounted on rails 5 and a robotic arm 6. The arm is constructed of rigid members connected by revolute joints. The arm is rotatable with respect to the base 4 and includes revolute joints at the shoulder, elbow and wrist with rigid links extending between the revolute joints.

It will be appreciated that the robots illustrated are purely exemplary and any type of robot having a robotic arm may be used. Also, it will be appreciated that the principles of the invention are not limited to industrial robots for manufacturing industry, and robots suitable for a variety of applications, e.g. medical surgery, may employ the invention. The robot arrangement may include any number of robots may be used, each having one or more robotic arms, however the robot arrangement must include at least two robotic arms.

At the distal end of each robotic arm 6, beyond the wrist joint, is an engagement interface 7 for attachment to either an end-effector or an end-effector carrier adapted to carry an end-effector. Industrial robots may carry a variety of end-effectors for performing operations in the environment, or zone, of the robot arrangement. For example, one end-effector may be a pick-and-place device, another a drill, and a third a spot welding unit. However, it will be appreciated by those skilled in the art that end-effectors for industrial applications may take a variety of other forms depending upon the tasks to be performed.

As shown in figure 1, the robots 1, 2, 3 are disposed in a robot zone indicated generally at 8, and the robots within that zone collectively form the robot arrangement. It will be appreciated that the robots may be constrained to operate within that robot zone or may be free to move into and out of that robot zone. In the configuration shown in figure 1, each of the robots 1, 2, 3 may be controlled independently for performing independent operations within the robot zone. In addition two or more of the robots may be controlled together in a synchronised manner to perform a particular operation within the robot zone. For example, robots 1 and 2 may be controlled to grip either end of a work piece and robot 3 may be controlled to perform a drilling operation on the work piece held by robots 1 and 2. In this 'separate' mode of operation of the robot arrangement it is important to note that whilst the movements of the three robots 1, 2, 3 may be synchronised so as to complete a particular operation in the robot zone, the positional accuracy of each robot end-effector is a function of the available accuracy of each individual robot. Due to the cantilever effect of the distal end of the arm with respect to the base, the play inherent in the robot arm will limit the available accuracy of even the most advanced modern robots.

When a precision operation, such as a precision drilling operation for example, needs to be conducted for high-end manufacturing sectors such as aerospace industry, the three robots 1, 2, 3 can operate in a 'collaborative' mode in which the three robot arms join together as one to perform an operation. Each robot will initially lay down the end-effector (if any) connected to thereby freeing i.e. leaving disengaged its engagement interface 7. One of the robots, in this instance the first robot 1, will then pick up an end-effector carrier 8 as shown schematically in figure 2. The end-effector carrier 8 in this first example has a triangular prism shape. The three faces (between the top and bottom sides) of the end- effector carrier 8 have a respective engagement interface 9a, 9b, 9c for engagement with the respective engagement interfaces 7 of the robots 1, 2, 3. Once the first robot 1 has picked up the end-effector carrier 8 one or more of the robots move (along rails 5 not shown in figure 2) to an area where the other two robots 2, 3 can connect to the end-effector carrier 8. The engagement interfaces 7, 9a-c between the robots 1, 2, 3 and the end-effector carrier 8 are configured to provide positive engagement, i.e. a holding engagement not a mere abutment of the engagement interfaces when engaged. This positive holding engagement allows lateral load to be transferred between the robots 1, 2, 3 such that the stability and therefore accuracy of the coupled robots is greater than the accuracy of any individual robot by itself.

Figure 3 illustrates the robot arrangement following coupling of all three robots 1, 2, 3 directly to the same end-effector carrier 8. As can be seen, the three robots are generally opposing one another. The end-effector carrier 8 carries an end-effector such as a drill, for example (not shown in the schematic views of figures 2 and 3 but shown in detail in figure 4). The three robots 1, 2, 3 coupled directly to the single end- effector carrier 8 as shown in figure 3 are operable to perform a precision operation, in this case a precision drilling operation.

The robots 1, 2, 3 are computer controlled in a conventional manner and a computer (not shown) will additionally control the synchronisation of the robots 1, 2, 3 in a non- conflicting manner. Preferably this is done by a master-slave relationship. One of the robots, which will typically be first robot 1 which picked up the end-effector carrier 8 first, will be designated as master and the other two robots 2, 3 will be designated as slaves. So long as the dimensions of the end-effector carrier 8 are known to the computer, the computer controlling movement of the master robot 1 will be able to compute in real time the required movement of the slave robots 2, 3 such that the robot arms 6 of the three robots are moveable in unison in a non-conflicting manner. The interfaces of the end-effector may be calibrated using either a basic teach mode or through active metrology such that the computer can store the relative dimensions of the end-effector interfaces.

It is intended that the controlled movement of the three robots when joined in the collaborative mode impose minimal or zero load upon one another. Any external load imposed, e.g. from the end-effector whilst performing an operation, will be exerted upon each of the robots. This external load will be shared between the three robots thereby reducing the load imposed at the distal end of any one robot arm, so reducing the deflections of that robot arm which provides the improved positional accuracy of the end-effector of the joined robots during operations in the 'collaborative' mode.

When the precision drilling operation is completed, two of the robots (which may be the slave robots 2, 3 but may be any two of the robots) will detach from the end- effector carrier 8 and proceed to carry out other tasks by reverting to the 'separate' mode. The robot still holding the end-effector carrier 8 may either continue using it for performing other operations (to a lesser degree of accuracy than in the collaborative mode described above) or exchange it for another end-effector (or another end-effector carrier) to perform another operation. The robots 1, 2, 3 can reconnect the next time if such co-operation is required. Figure 4 illustrates the end-effector carrier 8 in detail and shows the three engagement interfaces 9a, 9b, 9c for detachable detachment to the engagement interfaces 7 at the distal end of the respective robot arms 6 of the three robots 1, 2, 3. The engagement interfaces 9a-c in this example are identical and so only the engagement interface 9a will described in detail below. The engagement interface 9a is a quick change engagement interface adapted for ready engagement and disengagement with the robot arm. The engagement interface 9a includes engagement features 10 for positive engagement with corresponding engagement features of the engagement interface 7 of the robot arm 6. These features may take a variety of forms, such as pins and sockets for example, and in the particular example shown in figure 4 the features 10 are automatic Schunk clamps from Schunk GmbH.

As an alternative to the clamping features 10 the positive engagement between the end-effector carrier 8 and the robot arm 6 may be effected by locking means, solenoid clamps, electro-magnetic holding devices or any other suitable means. What is important is that the engagement interfaces 9a, 7 enable a positive holding engagement such that lateral load may be transferred in both directions between the robot arm and the end-effector carrier such that the robots can impart a stabilising effect upon each other when joined in the collaborative mode.

The engagement interface 9a further includes electrical connections 11 for the transfer of power and/or data between the end-effector carrier 8 and the robot arm 6. The number and arrangement of pins in the electrical connector 11 may vary depending on requirements. In the particular example illustrated in figure 4 the electrical interface is a modular connector, such as the Combitac produced by Multi-Contact AG. The engagement interface 9a is fixed with respect to the central body 12 of the end- effector carrier.

As shown in figure 4, the end-effector carrier 8 has an integral end-effector 13, which in this particular example is a drill end-effector for performing drilling operations. It will be appreciated that any type of end-effector 13 may be provided integral with the end-effector carrier 8 depending upon requirements. However, the drilling end- effector is particularly well suited to the high accuracy operations made possible in the collaborative mode since it is in drilling applications where the particularly high degree of accuracy, not currently achievable with existing robots, finds particular utility.

The ability of the robots in the robot arrangement to operate in the collaborative mode may eliminate the need for employing costly precision machinery, as the robot arrangement is able to perform the same task to a similar or higher level of accuracy. The principles of the invention can be built in to new robot arrangements, or may be applied retrospectively to existing robot arrangements where robots can come within proximity of each other.

Figure 5 illustrates a second example of the end-effector carrier 18 which is substantially identical to the end-effector carrier 8 with the exception that it does not have an integrated end-effector. In all other respects the end-effector carrier 18 is identical to the end-effector carrier 8 described above and so a detailed description of common parts will not be repeated here. The end-effector carrier 18 on its underside includes an end-effector engagement interface (not shown) for detachable attachment to a variety of interchangeable end-effectors.

The engagement interfaces between the robot and carrier and between the carrier and end-effector may be the same or may be different. The end-effector engagement interface 19 may be a quick-connect engagement interface to allow ready interchange between the various end-effectors. The end-effector carrier 18 may be picked up by one of the robots and then moved to pick up a suitable end-effector or alternatively the robot may pick up the end-effector carrier 18 having an appropriate end-effector already attached thereto. Once the first robot has picked up the end-effector carrier 18 with the end-effector attached then the end-effector carrier 18 may be coupled to the other two robots for performing the collaborative precision operation as described above.

Whilst in the above described examples the end-effector carriers 8, 18 have a generally triangular prism shape, the end-effector carrier may alternatively take a variety of other shapes. Figure 6 illustrates a third example in which the end-effector carrier 28 has a generally triangular base pyramid shape and figure 7 illustrates a fourth example in which the end-effector carrier 38 has a generally cube shape. It will be appreciated that the end-effector carrier may take a variety of other forms and may generally be any polyhedron.

The end-effector carrier 28 of the third example shown in figure 6 having the generally pyramid shape may provide even greater stability during precision operations than the carriers 8 or 18, particularly during drilling operations, since the robot arms can react against loads transmitted upwardly along the drilling axis. The engagement interfaces (for engagement with either an end-effector or a robot arm) are preferably provided on every face of the end-effector carrier. The end-effector carrier equipped with an end-effector may be adapted to perform operations in any desired direction including upwards. To that end, in a further example the end-effector carrier may take an inverted triangular base pyramid shape with the apex facing generally downwardly for performing upward operations.

As shown in figure 7, not all engagement interfaces of the end-effector carrier need have a robot arm directly coupled to it during the collaborative mode. The end- effector carrier 38 has four faces 39a-d each having an engagement interface for coupling directly to a respective robot arm. However, only three robots 1, 2, 3 are coupled to the end-effector carrier 38 via the engagement interfaces 39a-c whilst the fourth engagement interface 39d is left uncoupled.

It is currently envisaged that a combination of three robots spaced approximately equidistant from the end-effector and spaced at equal angles from one another may provide the optimal combination of end-effector stability and operational flexibility in the collaborative mode. However, it will be appreciated that any two or more robots may be directly coupled to a single end-effector carrier to perform the precision operation in the collaborative mode. Where only two robots are used, the additional stability promoted by the collaborative mode may be optimal if the two robots are spaced equidistant and directly opposite each other. However, regardless of the angles and the spacing, the use of more than one robot directly coupled to the end-effector carrier may help reduce the effects of vibration during operations in the collaborative mode. Using the end-effector 38 shown in figure 7, two, three or even four robots may be combined by coupling directly to the single end-effector carrier 38. Each robot will be generally opposing the other robots. Additionally, while several robots may be within the same robot zone 8 not all robots may be used in the collaborative mode. For example, if only two of the three robots 1, 2, 3 in the robot zone 8 shown in figure 1 are used in the collaborative mode, the other robot may provide operational support to the connected robots, e.g. supplying and removing work pieces.

It will further be appreciated that not all of the robots in the robot zone need be of the same type in order to work in the collaborative mode. All that is required is that they have a suitable engagement interface 7 for connecting to the end-effector carrier. To this end, it will be appreciated that whilst in the first example end-effector carrier 8 shown in figure 4 the engagement interfaces 9a-c are identical, this need not be the case and the engagement interfaces of the end-effector carrier 8 may instead be different for co-operating with engagement interfaces of respective different robots arms.

Furthermore, it will be appreciated that robots other than 6-axis jointed arm robots may be used and these may be located on a base that is moveable in a manner other than sliding such as depicted in figure 1. For example, robots mounted upon wheeled bases may be used. Whilst in the above described examples of the first embodiment each of the robots 1, 2, 3 have an engagement interface 7 for detachable attachment to the end-effector carrier 8, in an alternative embodiment the end-effector carrier may be fixed to the distal end of the arm of one of the robots. The robot having the fixedly attached end- effector carrier then performs all operations using that end-effector carrier. The end- effector carrier may have an integral end-effector or may have an engagement interface for exchanging end-effectors so as to increase the flexibility of the robot. The end-effector has at least one engagement interface for detachable attachment to another robot arm.

When it is desired that the robot having the fixed end-effector carrier operates in the collaborative mode, the other robot(s) having the engagement interface 7 are moved into position so as to be coupled to the engagement interfaces of the end-effector carrier. The two or more robots now coupled together can perform the collaborative precision operation in an identical manner to that described above. Upon completion of the precision operation the other robots can detach from the end-effector carrier as before and the robot having the fixed end-effector carrier can then proceed with performing operations separately from the other robots.

In a further alternative, a single end effector carrier may be fixedly attached to the distal ends of a plurality of robot arms. In such a robot arrangement the flexibility is reduced as the robot arrangement always operates in the collaborative mode, and cannot operative in the separate mode, but robot arrangement can perform the high precision operations described above.

Figures 8 and 9 illustrate an extension of the fixed end-effector carrier in accordance with a second embodiment of the invention. As shown in figure 8 the three robots 1, 2, 3 each have an end-effector carrier 48 fixed to the distal end of the arm 6 of the respective robots. In figure 8 the end-effector carriers 48 are physically decoupled from one another such that the robots 1, 2, 3 are operable in the 'separate' mode to perform operations within the robot zone. Each end-effector carrier 48 has one fixed engagement interface fixedly attached to the distal end of its respective robot arm 6 and three releasable engagement interfaces on the other three faces of the cube between the top and bottom sides. The releasable engagement interfaces are configured for detachable attachment to the releasable engagement interfaces of the other end-effector carriers 48.

Figure 9 shows the robot arrangement with the three end-effector carriers 48 coupled together such that the robots 1, 2, 3 are directly coupled together via their end-effector carriers 48 ready to perform operations in the 'collaborative' mode. The robots can be computer controlled in a master-slave relationship as before. Since each of the three end-effector carriers 48 may carry an end-effector any one of the end-effectors may be used for performing a particular operation in the collaborative mode. In an alternative embodiment, an end-effector carrier may have one or more engagement interfaces for coupling to the distal end of a respective robot arm, and one or more engagement interfaces for coupling to a neighbouring end-effector carrier.

In any of the above embodiments the distal end of the robot arms may be used not only to pick up end-effectors and/or end-effector carriers, but may also be used to pick up and position tool stands on which they can subsequently work collaboratively.

It will be appreciated that in the collaborative mode the robots which are joined together retain the ability to move, e.g. their bases, arms, etc, although this movement will be somewhat limited due to the coupling of the robot arms. Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. An end-effector carrier for a robot arrangement, the end-effector carrier comprising: a first engagement interface configured for attachment to a distal end of a first robot arm; a second engagement interface configured for attachment to either a distal end of a second robot arm or to a second end-effector carrier; and either: i) an end-effector integral with the end-effector carrier, the end-effector being configured to perform at least one operation in the environment of the robot arrangement, or ii) an end-effector engagement interface for detachable attachment to an end- effector configured to perform at least one operation in the environment of the robot arrangement.

2. An end-effector carrier according to claim 1, wherein the first engagement interface is configured for fixing to the distal end of the first robot arm.

3. An end-effector carrier according to claim 1, wherein the first engagement interface is configured for detachable attachment to the distal end of the first robot arm.

4. An end-effector carrier according to claim 3, wherein the first engagement interface includes one or more features for coupling to corresponding feature(s) at the distal end of the first robot arm.

5. An end-effector carrier according to claim 3 or claim 4, wherein the first engagement interface includes electrical connections for cooperating with corresponding electrical connections at the distal end the first robot arm for power and/or data transfer.

6. An end-effector carrier according to any of claims 1 to 5, wherein the second engagement interface is configured for fixing to said distal end of the second robot arm or said second end-effector carrier.

7. An end-effector carrier according to any of claims 1 to 5, wherein the second engagement interface is configured for detachable attachment to said distal end of the second robot arm or said second end-effector carrier.

8. An end-effector carrier according to claim 7, wherein the second engagement interface includes one or more features for coupling to corresponding feature(s) of either the distal end of the second robot arm or the second end- effector carrier.

9. An end-effector carrier according to claim 8, wherein the second engagement interface includes electrical connections for cooperating with corresponding electrical connections for power and/or data transfer.

10. An end-effector carrier according to any of claims 1 to 9, further comprising a plurality of the first engagement interfaces configured for attachment to respective first robot arms and/or a plurality of the second engagement interfaces for attachment to respective second robot arms or second end- effector carriers.

11. An end-effector carrier according to any of claims 1 to 9, wherein the carrier is multi-faceted, and the first and second engagement interfaces are provided on respective faces of the multi-faceted carrier.

12. A robot arrangement comprising: a plurality of robot arms each having a distal end; and the end-effector carrier of any of claims 1 to 11.

13. A robot arrangement comprising: a plurality of robot arms each having a distal end; and at least one end-effector carrier attached or attachable to the distal end of at least one robot arm and configured to carry an end-effector for performing one or more operations in the environment of the robot arrangement, wherein the robot arrangement is operable in a first mode in which first and second robot arms of the plurality of robot arms are coupled together either: i) by coupling of their respective distal ends to only one end-effector carrier, or ii) by direct coupling together of end-effector carriers attached to the distal ends of the respective robot arms, such that the first and second robot arms are moveable in unison, and a second mode in which the first and second robot arms are decoupled from each other such that the first and second robot arms are moveable separately.

14. A robot arrangement according to claim 13, wherein the end-effector carrier is detachably attachable to the distal end of the first robot arm.

15. A robot arrangement according to claim 14, wherein the end-effector carrier is detachably attachable to respective distal ends of each of the plurality of robot arms.

16. A robot arrangement according to claim 14 or 15, wherein the detachable attachment is effected by cooperating engagement interfaces on the end- effector carrier and on the distal end of the robot arm.

17. A robot arrangement according to claim 16, wherein the engagement interfaces effect a mechanical inter-engagement between the end-effector carrier and the distal end of the robot arm.

18. A robot arrangement according to claim 16 or claim 17, wherein the engagement interfaces include electrical connections for power and/or data transfer.

19. A robot arrangement according to claim 13, wherein the end-effector carrier is fixed to the distal end of the first robot arm.

20. A robot arrangement according to claim 19, wherein the end-effector carrier is detachably attachable to the distal end of the second robot arm.

21. A robot arrangement according to claim 20, wherein the detachable attachment is effected by cooperating engagement interfaces on the end-effector carrier and on the distal end of the second robot arm.

22. A robot arrangement according to claim 21, wherein the engagement interfaces effect a mechanical inter-engagement between the end-effector carrier and the distal end of the second robot arm.

23. A robot arrangement according to claim 21 or claim 22, wherein the engagement interfaces include electrical connections for power and/or data transfer.

24. A robot arrangement according to claim 13, wherein a respective end-effector carrier is fixed to the distal ends of at least the first and second robot arms of the plurality of robot arms.

25. A robot arrangement according to claim 24, wherein the end-effector carriers are detachably attachable to each other, such that in the first mode the end- effector carriers of the first and second robot arms are directly coupled together, and in the second mode the end-effector carriers of the first and second robot arms are decoupled from each other.

26. A robot arrangement according to claim 25, wherein the detachable attachment is effected by cooperating engagement interfaces on the respective end-effector carriers.

27. A robot arrangement according to any of claims 12 to 26, further comprising a plurality of robots each having at least one of the robot arms.

28. A robot arrangement according to any of claims 12 to 26, further comprising a single robot having the plurality of robot arms.

29. A robot arrangement according to claim 27 or claim 28, wherein the robot arms are 6-axis jointed arms.

30. A robot arrangement according to any of claims 27 to 29, wherein the robot(s) has/have a base adapted for movement across a robot zone of the robot arrangement.

31. A robot arrangement according to any of claims 12 to 30, further comprising an end-effector fixed to each end-effector carrier for performing one or more operations in the environment of the robot arrangement.

32. A robot arrangement according to any of claims 12 to 30, further comprising an end-effector detachably attachable to each end-effector carrier for performing one or more operations in the environment of the robot arrangement.

33. A robot arrangement according to claim 32, wherein the detachable attachment is effected by cooperating engagement interfaces on the end-effector and on the end-effector carrier.

34. A robot arrangement according to claim 32 or claim 33, wherein the end- effector is one selected from a group of inter-changeable end-effectors.

35. A robot arrangement according to any of claims 13 to 34, wherein in the first mode of operation one of the coupled robot arms is designated as master and the other coupled robot arm(s) is/are designated as slave for the movement in unison.

36. A method of operating a robot arrangement, the method comprising: providing a plurality of robot arms each having a distal end; providing at least one end-effector carrier attached to the distal end of at least one robot arm and configured to carry an end-effector for performing one or more operations in the environment of the robot arrangement; operating the robot arrangement in a first mode by: coupling together first and second robot arms of the plurality of robot arms either: i) by coupling of their respective distal ends to only one end-effector carrier, or ii) by direct coupling together of end-effector carriers attached to the distal ends of the respective robot arms, and moving the first and second robot arms in unison, and operating the robot arrangement in a second mode in which the first and second robot arms are decoupled from each other, by moving the first and second robot arms separately.

37. A method according to claim 36, further comprising detaching the end-effector carrier from the distal end of the first robot arm.

38. A method according to claim 36, further comprising attaching a single end- effector carrier directly to respective distal ends of a plurality of robot arms in the first mode.

39. A method according to claim 36, further comprising attaching a respective end-effector to each of a plurality of robot arms, and coupling the end-effectors together in the first mode.

40. A method according to any of claims 36 to 39, further comprising designating one of the coupled robot arms as master and designating the other coupled robot arm(s) as slave to follow movement of the master in the first mode of operation.

41. A method according to any of claims 36 to 40, further comprising using an end-effector carried by the end-effector carrier coupled to the plurality of robot arms to perform an operation in the environment of the robot arrangement during the first mode of operation.

42. A method according to any of claims 36 to 41, further comprising using an end-effector coupled to one of the robot arms to perform an operation in the environment of the robot arrangement separate from the position or movement of the other robot arms of the robot arrangement during the second mode of operation.

43. A robot arrangement comprising: a plurality of robot arms each having a distal end; and a single end-effector carrier fixedly attached to the distal ends of the plurality of robot arms and configured to carry an end-effector for performing one or more operations in the environment of the robot arrangement, wherein the robot arrangement is operable such that the first and second robot arms are moveable in unison.

44. A robot arrangement according to claim 43, wherein the robot arms are 6-axis jointed arms.

45. A robot arrangement according to claim 43 or claim 44, further comprising an end-effector fixed to the end-effector carrier for performing one or more operations in the environment of the robot arrangement.

46. A robot arrangement according to claim 43 or claim 44, further comprising an end-effector detachably attachable to the end-effector carrier for performing one or more operations in the environment of the robot arrangement.

47. A robot arrangement according to claim 46, wherein the detachable attachment is effected by cooperating engagement interfaces on the end-effector and on the end-effector carrier.

48. A robot arrangement according to claim 46 or claim 47, wherein the end- effector is one selected from a group of inter-changeable end-effectors.

49. A robot arrangement according to any of claims 43 to 48, wherein one of the robot arms is designated as master and the other robot arm(s) is/are designated as slave for the movement in unison.

50. A method of operating the robot arrangement of any of claims 43 to 49, the method comprising: moving the plurality of robot arms in unison.

51. A method according to claim 50, further comprising designating one of the robot arms as master and designating the other coupled robot arm(s) as slave to follow movement of the master.

52. A method according to claim 50 or claim 51, further comprising using an end- effector carried by the end-effector carrier to perform an operation in the environment of the robot arrangement.