WO2018036634A1

WO2018036634A1 - A parallel kinematics robot with a telescopic shaft

Info

Publication number: WO2018036634A1
Application number: PCT/EP2016/070141
Authority: WO
Inventors: Daniel LUNDBÄCK
Original assignee: Abb Schweiz Ag
Priority date: 2016-08-26
Filing date: 2016-08-26
Publication date: 2018-03-01

Abstract

A parallel kinematics robot (1) comprising a base section (3), an end effector (5) and at least one telescopic shaft (7) arranged between the base section and the end effector. The telescopic shaft comprises an inner shaft (13) and an outer tube (11) arranged externally on the inner shaft. The telescopic shaft comprises at least one set of coupling members, comprising a first coupling member (21; 31; 41) provided internally on the outer tube (11) and a second coupling member (22; 32; 42) provided externally on the inner shaft (13). Said first and second coupling members are configured to transmit torque between the outer tube and the inner shaft, and they are configured for axial sliding engagement with each other. The second coupling member is configured to extend at least partly outside of the outer tube during operation of the telescopic shaft.

Description

A PARALLEL KINEMATICS ROBOT WITH A TELESCOPIC SHAFT

Technical field of the invention

The present invention relates to a parallel kinematics robot having a telescopic shaft. The parallel kinematics robot comprises a base section and an end effector. The telescopic shaft is arranged between the base section and the end effector, and opposite ends of the telescopic shaft are respectively connected with the base section and the end effector.

Background

Industrial robots according to the concept of parallel kinematic robots are previously known. Such robots are mainly used for picking and placing fairly small objects. An example of parallel kinematics robots are robots built according to the delta concept, so called delta robots, which are previously known from for example US 7188544 and EP 2301726. Delta robots are for example used in the food industry, in the field of surgery and medical science, in the pharmaceutical industry, and many other fields. They are for example used for transferring pieces of chocolate or similar objects from a moving conveyor belt to a predetermined location such as in a packaging box, with high speed and precision. The ability to be able to handle small and delicate objects with great speed and precision is important for automation of industrial processes.

A delta robot commonly comprises an arm system comprising a base section, a movable plate and several jointed pullrods joining the base section to the movable plate. The pullrods function as arms by means of which the movable plate can be moved in space. The movement of a pullrod is controlled by a motor usually located at the base section. An end effector, such as a rotatable tool or a gripping device, can be attached to the movable plate. In order to operate the tool or gripping device, a motor is usually located in the base section. The rotation of a tool should be possible to carry out in free space, e.g. with three degrees of freedom. Thus the distance from the base section to the movable plate and the tool is variable. A telescopic shaft is therefore arranged between the base section and the tool, which shaft acts as a driving shaft from the motor to the tool. This telescopic shaft is sometimes called a fourth axle. The telescopic shaft is normally mounted in bearings in the movable plate, and it can drive the tool directly or via a gearing arrangement located at the movable plate. In some

applications, more than one telescopic shaft is used.

The telescopic shaft of the delta robot must be able to decrease or increase its length at the same time as it must transfer relatively high torque with great precision and operate at a considerable speed. One general problem with delta robots is how to handle friction and loose play between the different parts of the arm system that arises during the operation of the robot. Moreover, delta robots are often used in environments where there are high demands on hygiene.

According to US 7188544, telescopic arms for industrial robots are known wherein an outer tube is joined to an inner axle with an ordinary sliding joint, in the form of splines or similar means. In US 7188544 is proposed an improvement wherein a pair of end-to-end torsional rigid bushings is arranged on the outer tube in which the inner axle is mounted to be displaceable. Thus transfer of torque is obtained between the inner axle and the outer tube via the bushings. At the same time friction and loose play is minimized between the inner axle and the outer tube. The inner axle has axial grooves that guide the inner axle during displacement in the bushings. Ball bearings are placed in the grooves on the inner axle and arranged within the bushings. It is also provided for lubrication of the inner axle.

From EP2301726 is previously known a telescopic shaft for a delta robot wherein an inner arm is guided in the outer arm by a sliding bushing forming a head portion of the inner arm. The outer arm has a square cross section. The bushing has a plurality of elastically deformable radial tongues that extends into the corners of the outer tube and thereby is obtained a clearance-free guide means with reduced friction and at the same time a rigid torsional coupling between the inner arm and the outer arm. The bushings are preferably made of some kind of plastic.

Today's telescopic shafts for parallel kinematics robots such as delta robots are mainly made of metal such as aluminium. As a result, they are sometimes not allowed in wet environments. Further, they comprise a number of parts that must be mounted together which is a disadvantage as such and may also entail disadvantages from a hygienic point of view. The combined requirement for good transfer of torque and low friction in relative linear movement results in high demands on precision and materials, which do not come cheap.

Summary of the invention

An object of the invention is to provide an improved parallel kinematics robot having a telescopic shaft that fulfils high requirements for transfer of torque and at the same time makes it possible to have a simplified construction.

A further object is to provide a parallel kinematics robot with a telescopic shaft that makes it possible to use the parallel kinematics robot in wet environments and environments with high hygienic demands.

These objects are achieved by the parallel kinematics robot according to appended claim 1 and a method according to claim 14.

The invention is based on the realization that by altering the design of coupling members that are used to couple the outer tube to the inner shaft, many advantages can be obtained compared to prior art. According to a first aspect of the invention, there is provided a parallel kinematics robot comprising a base section, an end effector and at least one telescopic shaft arranged between the base section and the end effector, wherein opposite ends of the telescopic shaft are respectively connected with the base section and the end effector, wherein the telescopic shaft comprises an inner shaft and an outer tube arranged externally on the inner shaft, wherein the telescopic shaft comprises at least one set of coupling members comprising a first coupling member provided internally on the outer tube and a second coupling member provided externally on the inner shaft, wherein said first and second coupling members are configured to transmit torque between the outer tube and the inner shaft, wherein said first and second coupling members are configured for axial sliding engagement with each other, and wherein the second coupling member is configured to extend at least partly outside of the outer tube during operation of the telescopic shaft.

By having the coupling members configured for sliding engagement with each other, it is possible to eliminate the use of any bearings such as ball bearings where the coupling members are in contact with each other. This will make the design more simple with fewer parts. Further, by having the second coupling member of the inner shaft configured to extend outside of the outer tube during operation, it will be possible to arrange the first coupling member, which is provided internally on the outer tube, at the end of the outer tube from which the inner shaft extends. Thus the transmission of torque between the two coupling members, and thus between the outer tube and the inner shaft, will always occur at said end of the outer tube, or at least in the vicinity of said end. This will also make the first coupling member of the outer tube less complicated to clean and it will be easier to check in case of default. The inner shaft and the outer tube are usually arranged coaxially.

The parallel kinematics robot may for example be an industrial robot of the delta type. The parallel kinematics robot may have one telescopic shaft or more than one telescopic shaft.

According to one embodiment is defined a robot wherein the first coupling member of the outer tube may be arranged at an end of the outer tube from which the second coupling member extends during operation of the telescopic shaft. The advantage of this is already discussed above. The axial length of the first coupling member may be in the order of 5-20% of the total axial length of the second coupling member. It is also conceivable that the axial length of the first coupling member is essentially equal to the axial length of the second coupling member.

According to one embodiment is defined a robot wherein the second coupling member of the inner shaft may extend a major part of the telescoping length of the inner shaft. By telescoping length is meant the longitudinal length of the inner shaft that can be inserted into the outer shaft in a telescoping manner. This will make it possible to have a first coupling member of the outer tube that only extends a limited length at the end of the outer tube from where the second coupling member extends during operation of the telescopic shaft. Preferably, the second coupling member extends for essentially the entire telescoping length of the inner shaft.

According to one embodiment is defined a robot wherein the first coupling member may be configured to be projecting from an internal surface of the outer tube and/or the second coupling member may be configured to be projecting from an external surface of the inner shaft. By having coupling members that project from the respective surface of the inner shaft and/or outer tube it will be possible to have a more open structure that for example will be easy to clean. It may also be advantageous from a manufacturing point of view, since such a structure may be suitable for an extrusion process. Both the first and the second coupling member may be configured to be projecting outwards from the respective surface. By projecting outwards from the surface is meant that coupling member extends out and away from the surface, e.g. in the basic shape of a rib. The respective coupling members preferably extend in the longitudinal direction of the inner shaft and the outer tube respectively, i.e. axially.

As another alternative embodiment, one of the coupling members may be configured as projecting inwards from the concerned surface while the other coupling member is configured to project outward form the concerned surface. By projecting inwards from the surface is meant that the coupling member extends into the surface, into whatever is

underneath the surface, e.g. in the basic shape of a groove. Thus, the first coupling member may be configured to be projecting from an internal surface of the outer tube and the second coupling member may be configured as a groove in an external surface of the inner shaft. As a further alternative, the second coupling member may be configured to be projecting from an external surface of the inner shaft and the first coupling member is configured as a groove in an internal surface of the outer tube.

According to another embodiment is defined a robot wherein the first coupling member and/or the second coupling member may be configured to be elastically deformable. This will contribute to make it possible to have a small pre-tension between the coupling members in order to eliminate or at least reduce the occurrence of play between the coupling members and backlash during torque transmission.

According to yet another embodiment, the first and second coupling members may be configured with a respective geometrical shape configured to provide a rotationally interlocking engagement between said first and second coupling member when they are in sliding engagement with each other. By rotationally interlocking engagement is meant that, when the first coupling member and the second coupling member are in engagement, i.e. engaged with each other, they have such a geometrical shape that they are locked in relation to each other in the rotational direction, i.e. locked against relative rotation. This has the advantage that the torsional rigidity in the coupling between the respective coupling members and thus between the outer tube and the inner shaft is improved. It may be possible to obtain a torsionally rigid coupling between the outer tube and the inner shaft.

Further, according to one embodiment, the first coupling member may be integral with the outer tube. By integral is meant that the coupling member and the outer tube are manufactured in one piece and of the same material. This has the advantage that no loose and separate coupling members must be handled and mounted on the outer tube. It also has the advantage that a simple manufacturing method may be used, e.g. extrusion in a plastic material.

According to one embodiment, the second coupling member may be integral with the inner shaft. This has advantages corresponding to when the first coupling member is made integral with the outer tube.

According to yet another embodiment a robot is defined wherein a contact surface of the first coupling member and/or a contact surface of the second coupling member may be made of a low friction material.

Advantageously, the first coupling member and/or the second coupling member may be made of a low friction material.

Advantageously, the inner shaft and/or the outer tube may be made of a low friction material. In such a case metals may be totally avoided which is usually a requirement for wet environments, and plastic materials may be used. By making the inner shaft including the second coupling member, i.e. when the coupling member is integral with the inner shaft, in a low friction material, it will also be possible to manufacture the inner shaft including one or more coupling members in one and the same manufacturing process, e.g. by extrusion. The same advantage is also valid for the outer tube when manufactured such that any first coupling member is integral with the outer tube.

According to one embodiment, the robot may be provided with at least two sets of coupling members. Three or four sets of coupling members may be advantageous. Preferably the coupling members are arranged symmetrically in relation to the centre axis of the outer tube and the inner shaft. They are preferably distributed symmetrically on the external surface of the inner shaft and on the internal surface of the outer tube.

It should be mentioned that the outer tube and the inner shaft do not necessarily need to have a circular cross section. It is conceivable that they have a different cross section, e.g. rectangular.

The described telescopic shaft of the robot also has the general advantage that the dimensions will be easy to scale up or down for different torque demands.

According to another embodiment the inner shaft comprises at least one second coupling member and/or the outer tube comprises at least one first coupling member, and said inner shaft and/or said outer shaft is manufactured by an extrusion process. This has the advantage of a simple and cost effective manufacturing process.

Further features and advantages of the invention will also become apparent from the following detailed description of embodiments.

Brief description of the drawings

The invention will now be described in more detail, with reference being made to the enclosed schematic drawings illustrating different aspects and embodiments of the invention, given as examples only, and in which:

Fig. 1 shows schematically an embodiment of a parallel kinematics robot, according to the invention,

Fig. 2 illustrates schematically an embodiment of a telescopic shaft according to the invention,

Fig. 3 is a schematical detail view of the embodiment of a telescopic shaft shown in Fig. 2,

Fig. 4 illustrates schematically another embodiment of a telescopic shaft according to the present invention,

Figs 5a and 5b illustrate another embodiment of a telescopic shaft according to the invention.

Elements that are the same or represent corresponding or equivalent elements have been given the same reference numbers in the different figures.

Detailed description

A parallel kinematics robot 1 is schematically illustrated in Fig. 1. The parallel kinematics robot may for example be an industrial robot of the delta type. The robot comprises the main components of a base section 3, an end effector 5 and a telescopic shaft 7 arranged between the base section 3 and the end effector 5. Opposite ends 8, 9 of the telescopic shaft 7 are respectively connected to the base section 3 and the end effector 5. The telescopic shaft 7 comprises an inner shaft 13 and an outer tube 1 1 arranged externally on the inner shaft 13.

Referring now also to Figs. 2-4, the telescopic shaft 7 comprises at least one set of coupling members 21 , 22, 31 , 32 comprising a first coupling member 21 , 31 provided internally on the outer tube 1 1 and a second coupling member 22, 32 provided externally on the inner shaft 13. In Fig. 3 is illustrated one embodiment of the coupling members 21 , 22 and in Fig. 4 is illustrated another embodiment of the coupling members 31 , 32. Said first and second coupling members 21 , 22, 31 , 32 are configured to transmit torque between the outer tube 1 1 and the inner shaft 13. The first and second coupling members 21 , 22, 31 , 32 are also configured for axial sliding engagement with each other. Thereby is also achieved axial sliding engagement between the outer tube 1 1 and the inner shaft 13. Further, the second coupling member 22, 32 is configured to extend at least partly outside of the outer tube 1 1 during operation of the telescopic shaft 7. In Fig. 2 is shown the telescopic shaft 7 in an extended state when in operation. The inner shaft 13 extends outside of the open end 24 of the outer tube 1 1 .

In the illustrated example of a parallel kinematics robot in Fig. 1 , also other components are illustrated, which are usually common to a parallel kinematics robot, but which are not affected by the present invention, and which do not form part of the inventive idea. Such components are further components of the arm system, of which the telescopic shaft 7 may be a part, comprising several control arms 17 that are connected at their lower ends to a movable plate 19 and which are used to control the movement of the movable plate 19. These control arms 17 may e.g. be designed as comprising jointed pullrods. For each arm 17 there is an actuator 18 arranged at the base section 3. The number of control arms may vary, but is usually three or four. The end effector 5 is mounted to the movable plate 19. The end effector 5 is driven by a motor 6 that is usually arranged at the base section 3. The telescopic shaft 7 is therefore arranged between the base section 3 and the end effector 5, and the telescopic shaft 7 acts as a driving shaft from the motor to the end effector. The telescopic shaft 7 is normally mounted in bearings in the movable plate 19, and it can drive the end effector 5 directly or via a gearing arrangement located at the movable plate. The end effector 5 can e.g. be a gripping or picking tool or some kind of rotatable tool. The parallel kinematics robot is controlled by a control system in a robot controller 10.

In Figs. 2 and 3 is illustrated a telescopic shaft 7 according to one embodiment of the present invention. The telescopic shaft comprises a first end 8 provided with a connection device that makes the telescopic shaft 7 connectable to a base section 3, and a second end 9 with a connection device that makes the telescopic shaft 7 the connectable to an end effector 5. As already mentioned, the telescopic shaft 7 comprises an inner shaft 13 and an outer tube 1 1 arranged externally on the inner shaft 13. In Fig. 3 is shown the open end 24 of the outer tube 1 1 , from which the inner shaft 13 extends during operation of the robot.

In the illustrated embodiment of Figs. 2 and 3, there is illustrated first coupling members 21 projecting from an internal surface 26 of the outer tube 1 1 and second coupling members 22 projecting from an external surface 28 of the inner shaft. Both the first coupling member and the second coupling member are projecting outwards from the respective surface. They may be described as having a basic shape of a longitudinal rib. The first and second coupling members 21 , 22 are configured with a respective geometrical shape that will provide a rotationally interlocking engagement between said first and second coupling member when they are mounted together. They are also configured to be in sliding engagement with each other, when they are mounted together. In the illustrated embodiment, the first coupling members 21 are configured having a tubular shape, and the tube may be provided with a longitudinal slit 27 as shown. The slit 27 contributes to the possibility of making the first coupling member 21 elastically deformable. The second coupling members 22 are also configured as having a tubular shape provided with a longitudinal slit 28, which is optional. Also here the slit 28 contributes to the possibility of making the second coupling member elastically deformable. The diameters of the second coupling members 22 are smaller than the diameters of the first coupling members 21 in order to make the second coupling members 22 insertable into the first coupling members 21 , whereby engagement is achieved between the first and the second coupling members. This engagement is an axial sliding engagement in order to achieve that the inner shaft 13 could slide axially inside the outer tube 1 1. The first coupling member 21 thus has a first contact surface 23 that is in sliding contact with a second contact surface 25 of the second coupling member 22. It can be foreseen that alternatively only the coupling member having the larger diameter is provided with a longitudinal slit in order to receive the coupling member having the smaller diameter. Naturally, the coupling members may be reversed such that the first coupling member of the outer tube can be configured as having the smaller diameter, and the second coupling member of the inner shaft can be configured as having the larger diameter.

In the embodiment in Figs. 2 and 3 the second coupling members 22 extend along the entire telescoping length of the inner shaft 13. The first coupling members 21 are arranged at the open end 24 of the outer tube 1 1 , from which the inner shaft 13 with its second coupling members 22 extend during operation of the telescopic shaft 7. The first coupling members 21 can be made much shorter than the second coupling members 22. The axial lengths of the first coupling members may be in the order of 5-20% of the axial lengths of the second coupling members. It is also conceivable that the axial lengths of the first coupling members are essentially equal to the axial lengths of the second coupling members.

Further, in the illustrated embodiment the respective cross sections of the outer tube and the inner shaft are illustrated as being circular, but they may also have other cross sections, e.g. one or both may have a rectangular cross section.

Both the first and the second coupling members, as well as the outer tube and the inner shaft are illustrated as having an open structure which is preferable, but it is also conceivable that they could be configured such that e.g. the coupling member with the smaller diameter is solid and also the inner shaft being solid.

In the embodiment of Figs. 2 and 3 there are four sets of coupling members 21 , 22. However, the number of sets of coupling members can be varied. Preferably the coupling members are arranged symmetrically in relation to the centre axis of the outer tube and the inner shaft. They are preferably distributed symmetrically on the external surface 28 of the inner shaft 13 and on the internal surface 26 of the outer tube 1 1 . In Fig. 4 is illustrated another embodiment of the first and second coupling members 31 , 32, in cross section. In this embodiment the second coupling members 32 are configured as arms projecting outwards from the external surface 38 of the inner shaft 13. Each arm abuts against a corresponding lug projecting outwards from the internal surface 36 of outer tube 1 1 , which lug form the first coupling member 31 . To this end, the first coupling member 31 has a first contact surface 33 that is in axial sliding contact with a second contact surface 35 of the second coupling member 32. In the illustrated embodiment, the arms and the lugs are arranged in pairs. Except for the geometrical cross sectional shape of the first and second coupling members, their configuration corresponds to the configuration of the coupling members of the first embodiment and the corresponding alternative configurations can be foreseen. Preferably, at least the second coupling members 32 are elastically deformable.

In Figs. 5a and 5b is schematically illustrated another alternative embodiment of a telescopic shaft 7 with coupling members. In this embodiment the second coupling member 42 is configured as a groove provided in the external surface 48 of the inner shaft 13, and the first coupling member 41 is configured as a rib projecting from the internal surface 46 of the outer tube 1 1 . Thus the second coupling member 42 projects inwards from the external surface 48 of the inner shaft, and the first coupling member 41 projects outwards from the internal surface 46 of the outer tube.

The embodiments of Figs, 4, 5a and 5b have the same functions as the embodiment of Figs. 2 and 3, and they can have corresponding configurations of details and corresponding variations.

In the illustrated embodiments, the first coupling members 21 , 31 , 41 of all

embodiments are illustrated as being integral with the outer tube 1 1 , thus are made in one piece with the outer tube. However, as an alternative it is also conceivable that they can be made as separate members attached to the outer tube. The same applies to the second coupling members 22, 32, 42 in relation to the inner shaft.

The contact surface of the first coupling member and/or the contact surface of the second coupling member may be made of a low friction material. By contact surface is meant a surface of the respective coupling member that is in contact with a corresponding surface of the other coupling member during the mentioned axial sliding engagement. By low friction material is meant a material having a friction coefficient of less than 0,2 when under load, or a so called plastic bearing material such as Teflon (PTFE), nylon, ultra high molecular weight polyethylene (UHMWP), acetal such as Delrin. Some of these materials may also be self-lubricating which is advantageous. Delrin has the advantage of being suitable for wet environments. Preferably, the material is a material that is approved by the US Food and Drug Administration. Either one or both of the outer tube with its coupling members and the inner shaft with its coupling members may be manufactured in an extrusion process. Alternatively, the first coupling member and/or the second coupling member may be made of a low friction material.

As another alternative, the inner shaft and/or the outer tube may be made of a low friction material.

In the illustrated embodiments, the inner shaft is illustrated as having a hollow interior and thus being shaped as a tube, but it is to be understood that the inner shaft may as well be a solid shaft or a partly solid shaft and that would be applicable to all of the described

embodiments without affecting any of the other described details.

The invention shall not be considered limited to the illustrated embodiments, but can be modified and altered in many ways, as realised by a person skilled in the art, without departing from the scope defined in the appended claims. Thus, the invention and in particular the design of the telescopic shaft is not limited in any way to the type of parallel kinematics robot described in the examples above or shown in the figures, but may also be applied to, for example, other types of parallel kinematics robots. Further, the parallel kinematics robot may have more than one telescopic shaft of the described type.

Claims

Patent Claims

1 . A parallel kinematics robot (1 ) comprising a base section (3), an end effector (5) and at least one telescopic shaft (7) arranged between the base section and the end effector, wherein opposite ends (8, 9) of the telescopic shaft are respectively connected with the base section and the end effector,

wherein the telescopic shaft comprises an inner shaft (13) and an outer tube (1 1 ) arranged externally on the inner shaft,

and wherein the telescopic shaft comprises at least one set of coupling members comprising a first coupling member (21 ; 31 ; 41 ) provided internally on the outer tube (1 1 ) and a second coupling member (22; 32; 42) provided externally on the inner shaft (13),

wherein said first and second coupling members (21 , 22; 31 , 32; 41 , 42) are configured to transmit torque between the outer tube (1 1 ) and the inner shaft (13),

wherein said first and second coupling members (21 , 22; 31 , 32; 41 , 42) are configured for axial sliding engagement with each other, and

wherein the second coupling member (22; 32; 42) is configured to extend at least partly outside of the outer tube (1 1 ) during operation of the telescopic shaft (7).

2. The robot according to claim 1 , wherein the first coupling member of the outer tube is arranged at an end (24) of the outer tube (1 1 ) from which the second coupling member (22; 32; 42) extends during operation of the telescopic shaft.

3. The robot according to any one of the preceding claims, wherein the second coupling member (22; 32; 42) of the inner shaft (13) extends for a major part of the telescoping length of the inner shaft.

4. The robot according to any one of the preceding claims, wherein the first coupling member (21 ; 31 ; 41 ) is configured to be projecting from an internal surface (26; 36; 46) of the outer tube and/or the second coupling member (22; 32; 42) is configured to be projecting from an external surface (28; 38; 48) of the inner shaft.

5. The robot according to any one of the preceding claims, wherein the first coupling member (41 ) is configured to be projecting outwards from an internal surface (46) of the outer tube (1 1 ) and the second coupling member (42) is configured as a groove in an external surface (48) of the inner shaft (13), or the second coupling member (32) is configured to be projecting outwards from an external surface (38) of the inner shaft (13) and the first coupling member (31 ) is configured as a groove in an internal surface (36) of the outer tube (1 1 ).

6. The robot according to any one of the preceding claims, wherein the first coupling member (21 ; 31 ; 41 ) and/or the second coupling member (22; 32; 42) is configured to be elastically deformable.

7. The robot according to any one of the preceding claims, wherein the first and second coupling members (21 , 22; 31 , 32; 41 , 42) are configured with a respective geometrical shape configured to provide a rotationally interlocking engagement between said first and second coupling member when they are in sliding engagement with each other.

8. The robot according to any one of the preceding claims, wherein the first coupling member (21 ; 31 ; 41 ) is integral with the outer tube (1 1 ).

9. The robot according to any one of the preceding claims, wherein the second coupling member (22; 32; 42) is integral with the inner shaft (13).

10. The robot according to any one of the preceding claims, wherein a contact surface (23; 33) of the first coupling member (21 ; 31 ) and/or a contact surface (25; 35) of the second coupling member (22; 32) is made of a low friction material.

1 1 . The robot according to any one of the preceding claims, wherein the first coupling member (21 ; 31 ; 41 ) and/or the second coupling member (22; 32; 42) is made of a low friction material.

12. The robot according to any one of the preceding claims, wherein the inner shaft (13) and/or the outer tube (1 1 ) is made of a low friction material.

13. The robot according to any one of the preceding claims, wherein it is provided with at least two sets of coupling members (21 , 22; 31 , 32; 41 , 42).

14. The robot according to any one of the preceding claims, wherein the inner shaft (13) comprises at least one second coupling member (22; 32; 42) and/or the outer tube (1 1 ) comprises at least one first coupling member (21 ; 31 ; 41 ), and wherein said inner shaft and/or said outer shaft is manufactured by an extrusion process.