Improvements in movable joints

Abstract

A movable joint 10 has sets of linkages 16, 18, 20, 22 connecting a first segment 12 and a second segment 14. The sets of linkages 16, 18, 20, 22 comprise a first motorised set of linkages 16 that is

Description

Technical Field of the Invention The present invention relates to movable joints, and in particular movable joints that may be incorporated in a robotic apparatus. Background to the Invention Prior singularity free movable joints for robotic manipulators such as the Omni Wrist (OW) or Quaternion joint (QJ) offer a degree of mobility. However, both of these prior joints are very complex and therefore difficult to manufacture. Their complex nature also means that the prior movable joints are cumbersome and require specialised cable management and transmission solutions. In addition, the large size of the joints mean they are not suited for accommodating within a manipulator. Further, both the OW and QJ joints have limited mobility in that their mobility is limited to a 2 degrees of freedom mobility envelope. It is an object of the present invention to obviate or mitigate at least one problem with prior moveable joints. Summary of the Invention According to a first aspect of the present invention, there is provided a movable joint comprising: a first segment; a second segment; and sets of linkages connecting the first and second segments, the sets of linkages comprising a first motorised set of linkages that is directly driven by a first motor. “Directly driven” in this patent specification means a direct drive mechanism mechanically connects a motor with the associated motorised part. The invention enables a movable joint with 3 degrees of freedom, thereby meaning the joint has improved mobility with respect to prior arrangements, allowing a tool mounted to the joint to move more freely. The present invention also provides a lightweight and compact movable joint where cables can be stored internally within the joint. The movable joint of the present invention is therefore particularly suited for use in an industrial robotic or medical manipulator. The joint of the present invention is also simplified with respect to prior arrangements, making manufacture of the joint easier. The joint provides good weight distribution meaning component parts may be 3D printed or made using simple casting / moulding techniques. A first direct drive mechanism may mechanically connect the first motor and the first motorised set of linkages. The first direct drive mechanism may not comprise one or more gears. The first direct drive mechanism may comprise a first rotatable drive shaft that extends along a first axis. The rotatable drive shaft may be directly coupled to the first motorised set of linkages. The first motorised set of linkages may pivot about the first axis. If in this patent specification a shaft is said to be “directly coupled” to another element there are no gears between that shaft and the element. The first segment may comprise the first direct drive mechanism and the first motor. The second segment may comprise a motorised rotatable element. The motorised rotatable element may be configured for a tool to be mounted thereto. The motorised rotatable element may be driven by a rotatable element motor. The rotatable element motor may be the motor associated with the motorised rotatable element. The motorised rotatable element may rotate about a rotatable element axis. The motorised rotatable element may be continuously rotatable about the rotatable element axis. The rotatable element may be continuously rotatable in a motor element rotational direction about the motorised rotatable element axis and an opposite motor element rotational direction about the motorised rotatable element axis. The rotatable element may be directly driven by the rotatable element motor. A rotatable element direct drive mechanism may mechanically connect the rotatable element motor and the motorised rotatable element. The motorised rotatable element direct drive mechanism may comprise a rotatable element drive shaft that extends co-directionally with the rotatable element axis. The motorised rotatable element motor may be fixed to the second segment. The motorised rotatable element motor may be directly fixed to the second segment. The motorised rotatable element may comprise a rotatable surface that faces away from a remaining portion of the joint. Advantageously, the motorised rotatable element enables a tool attached to the second segment to rotate, thereby providing an additional movement option for moving a tool mounted to the joint. This also provides additional corrective roll-motion discussed in detail later. The sets of linkages may comprise a second motorised set of linkages. The second motorised set of linkages may be driven by a second motor. A second drive mechanism may mechanically connect the second motorised set of linkages and the second motor. The second motor may be mounted on the first motor. The second motor may be mounted directly on the first motor. The second drive mechanism may comprise input and output shafts mechanically connected by gears. The output shaft may be directly coupled to the second motorised set of linkages. The gear ratio between the gears may be l:l(also known as a quasi-direct drive (QDDj). The second motorised set of linkages may be pivotable about a second axis. The second axis may always be orthogonal to the first axis during movement of the joint. The output shaft may extend along the second axis. The first segment may comprise the second motor and second drive mechanism. The first, second and / or rotatable element motors may be electric motors. The first and second motors may be electrically connected in series. The first, second and rotatable element motors may be electrically connected in series. The daisy chaining of the electrical components of the joint allows for better cable management within the joint. The first motor may be internally mounted within the joint. The second motor may be internally mounted within the joint. The rotatable element motor may be internally mounted within the joint. “Internally mounted” in this patent specification means that the internally mounted element is not mounted on an exterior surface of the joint. The sets of linkages may extend from the first segment to the second segment. The first segment may comprise a first body portion and the second segment may comprise a second body portion. The sets of linkages may define with the first and second body portions an internal space within the joint in which the first motor is located. The rotatable element motor may be located within the internal space. The second motor may be located within the internal space. The sets of linkages may comprise four sets of linkages. The sets of linkages may consist of four sets of linkages. The sets of linkages may comprise a non-motorised set of linkages. The sets of linkages may comprise first and second non-motorised sets of linkages. Each set of linkages may be articulated. The sets of linkages may comprise the first and second motorised sets of linkages and the first and second non-motorised sets of linkages. Each set of linkages may comprise three linkages. Each set of linkages may comprise an input linkage pivotably connected to the first segment, an output linkage pivotably connected to the second segment, and an intermediate linkage connecting the input and output linkages. The intermediate linkage may be pivotably connected to each of the input and output linkages. A first pivotal connection between the intermediate linkage and the input linkage may comprise a first bearing. A second pivotal connection between the intermediate linkage and the output linkage may comprise a second bearing. The input linkages of the sets of linkages may comprise first and second input linkage pairs of input linkages. Each of the input linkages of the first input linkage pair of input linkages may pivot about a first common input linkage pivot axis. Each of the input linkages of the second input linkage pair of input linkages may pivot about a second common input linkage pivot axis. The first common input linkage pivot axis may be orthogonal to the second common input linkage pivot axis. The first common input linkage pivot axis may be the first axis. The second common input pivot axis may be the second axis. A first input linkage distance between each input linkage of the first input linkage pair along the first common input pivot axis may be the same as a second input linkage distance between each input linkage of the second input linkage pair along the second common input pivot axis. The output linkages of the sets of linkages may comprise first and second output linkage pairs of output linkages. The first output linkage pair of output linkages may pivot about a first common output linkage pivot axis. The second output linkage pair of output linkages may pivot about a second common output linkage pivot axis. The first common output linkage pivot axis may be orthogonal to the second common output linkage pivot axis. The first common output linkage pivot axis and the second common output pivot axis may always be orthogonal to the rotational element axis. A first output linkage distance between each output linkage of the first output linkage pair along the first common output pivot axis may be the same as a second output linkage distance between each output linkage of the second output linkage pair along the second common output pivot axis. The input linkages may be pivotably connected to the first segment around an outer circumference of the first segment (the first segment outer circumference). The input linkages may be pivotably connected to the first segment around the first segment outer circumference of the first segment at first connection points. The first connection points may be substantially evenly arranged around the first segment outer circumference. When there are four sets of linkages each first connection point may be rotationally spaced apart from adjacent first connection points by a first rotational angle. The first rotational angle may be 90 degrees. The first segment outer circumference may be a first outer circumference of the first body portion. The output linkages may be pivotably connected to the second segment around an outer circumference of the second segment (the second segment outer circumference). The output linkages may be pivotably connected to the second segment around a second segment outer circumference of the second segment at second connection points. The second connection points may be substantially evenly arranged around the second segment outer circumference. When there are four sets of linkages each second connection point may be rotationally spaced apart from adjacent second connection points by a second rotational angle. The second rotational angle may be 90 degrees. The second segment outer circumference may be a second outer circumference of the second body portion. In a neutral position, the first and second segments may be positioned opposite one another. In the neutral position, the plane (a first segment plane) of the first segment may be parallel with the plane (a second segment plane) of the second segment. In the neutral position, centre points of the first and second segments may lie on a common axis (a segment centre point common axis). In the neutral position, the centre point (the first segment centre point) of the first segment may lie in the first segment plane and the centre point (the second segment centre point) of the second segment may lie in the second segment plane. In the neutral position, the sets of linkages may be spaced apart. In the neutral position, the intermediate linkages of the sets of linkages may be substantially parallel to one another. In the neutral position, intermediate linkages of the sets of linkages may be equally spaced from a centre point of the joint. In the neutral position, the intermediate linkages of the sets of linkages may be equally spaced from the rotatable element axis. In the neutral position, the second connection point of each set may be rotationally offset from the first connection point by an offset angle of 180 degrees. The rotatable element axis may be orthogonal to the first and second axes in the neutral position. In the neutral position, the rotatable element axis may be orthogonal to the first common input linkage pivot axis, the second common input linkage pivot axis, the first common output linkage pivot axis and / or the second common output pivot axis. In the neutral position, centroids of the first and second segments may lie on the rotatable element axis. Each of the linkages of each set may be curved. The intermediate linkages may be concave. In the neutral position, the intermediate linkages may curve inwardly towards the rotatable element axis. In the neutral position, the input linkages and output linkages may be convex. The input and output linkages may curve outwardly. In the neutral position, the input and output linkages may curve outwardly in a direction away from the rotatable element axis. In other words, in the neutral position, the input and output linkages may be concave to the rotatable element axis. In the neutral position, a first plane may comprise the rotatable element axis and the first common input linkage pivot axis. The rotatable element axis and the first common input linkage pivot axis may extend in the first plane. When the joint is viewed from a viewing position that is orthogonal to the first plane, the input linkage of a viewable set of linkages may extend from where it is pivotably connected to the first segment to the intermediate linkage of the viewable set of linkages along an input linkage axis, and the output linkage of the viewable set of linkages may extend from where it is connected to the second segment to the intermediate linkage along an output linkage axis, wherein the input linkage axis and output linkage axis may intersect each other at an intersection point. The viewable set of linkages may be symmetric to the intersection point when viewed from the viewing position. The intersection point may lie in a dividing plane that is orthogonal to the first plane and the viewable set of linkages may be symmetric about the dividing plane when viewed from the viewing position. A non-zero angle may be between the input and output axes. The non-zero angle may be an angle in the range of 30 to 80 degrees, preferably 40 to 70 degrees. In particular embodiments, the nonzero angle is 45 degrees. In other embodiments, the non-zero angle is 60 degrees. In the neutral position, each set of linkages may have the same configuration. The sets of linkages may have substantially the same construction. The motorised linkages may have substantially the same construction. The non-motorised linkages may have substantially the same construction. The input linkages of all the sets of linkages may have the same construction. The intermediate linkages of all the sets of linkages may have the same construction. The output linkages of all the sets of linkages may have the same construction. Each linkage may be elongate. Each linkage may comprise at least one longitudinally extending arm. Preferably, each linkage comprises first and second longitudinally extending arms that are substantially parallel to one another, wherein struts extend transversely between the first and second anus. The arms may extend between heads. Each head may be for receiving a pivot or comprise a pivot for inserting into a corresponding head. According to a second aspect of the present invention, there is provided an apparatus comprising: the movable joint of the first aspect; and a tool mounted on the second segment. The tool may be a grabber tool. The apparatus may be a manipulator. The manipulator may be a surgical manipulator. The manipulator may be an industrial robotic manipulator. The apparatus of the second aspect may incorporate all or some of the features of the movable joint of the first aspect as desired or appropriate. Detailed Description of the Invention In order that the invention may be more clearly understood one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 shows a movable joint; Figure 2A and figure 2B each show the same perspective view of the joint of Figure 1 without its internal components, for the sake of clarity each figure includes a different partial set of reference numerals; Figure 3 shows a side view of the joint of Figure 1 without its internal components; and Figure 4 illustrates the mobility of the joint of Figure 1. With reference to Figure I. there is shown a moveable joint 10 according to the present invention. The joint 10 is moveable in that it can move between different positions, allowing a tool mounted to the joint 10 to also move between different positions. As shown the joint includes first and second segments 12, 14 which are connected by sets of linkages 16, 18, 20, 22. In particular, in the depicted example, there are first and second sets of motorised linkages 16, 18 and first and second sets of non-motorised linkages. The first and second sets of motorised linkages 16, 18 are motorised in the sense that they are each allocated a motor, whereas the first and second sets of non-motorised linkages 20,22 are not motorised as each of these sets of linkages are not allocated a motor and are passively driven. Each set of linkages is preferably articulated. The first motorised set of linkages 16 is directly driven by a first motor 24 that is internally mounted within the joint. “Directly driven” in this patent specification means a direct drive mechanism mechanically connects a motor with the associated motorised part. In the depicted example, a first direct drive mechanism 26 mechanically connects the first motor 24 and the first motorised set of linkages 16. The first direct drive mechanism does not comprise one or more gears and a first rotatable drive shaft 26 of the first direct drive mechanism is shown in Figure 1. The first rotatable drive shaft extends along a first axis which is orthogonal to the plane in which the joint 10 is viewed in Figure 1. The rotatable drive shaft 26 may be directly coupled to the first motorised set of linkages 16. If in this patent specification a shaft is said to be “directly coupled” to another element, there are no gears between that shaft and the element. The first motorised set of linkages 16 are connected to the first rotatable drive shaft such that the first set of motorised linkages 16 may pivot about the first axis. The second motorised set of linkages 18 are driven by a second motor 30 and a second drive mechanism 32 mechanically connects the second motorised set of linkages 18 and the second motor 30. The second drive mechanism comprises input and output shafts mechanically connected by gears (although the input and output drive shafts are not visible in Figure 1 as they are obscured by other elements of the joint). In Figure 1, a gear 34 coupled to the input shaft is visible. The output shaft is preferably directly coupled to the second motorised set of linkages 18. The gear ratio between the gears that connect the input and output shafts is preferably 1:1, although other ratios can be provided if customisation is required. The second motorised set of linkages 18 are pivotable about a second axis, which corresponds to an output shaft axis of the output shaft. The second axis is always orthogonal to the first axis during movement of the joint. In the depicted example, the second motor 30 is directly mounted on the first motor 24, preferably by utilising one or more fasteners, so that the first and second motors are arranged in a stack which is internally mounted within the joint 10. Both the first and second motors 24, 30 are therefore internally mounted within the joint 10. “Internally mounted” in this patent specification means that the internally mounted element is not mounted on an exterior surface of the joint. The sets of linkages 16,18,20,22 extend from the first segment 12 to the second segment 14. The first segment 12 comprises a first body portion 36 and the second segment 14 comprises a second body portion 38. The sets of linkages 16, 18, 20, 22 define with the first and second body portions 36, 38 an internal space 43 within the joint in which the first and second motors 24, 30 are located. The output shaft of the second drive mechanism and the first rotatable drive shaft 26 of the first direct drive mechanism preferably extends through the first body portion 36. The second segment 14 comprises a motorised rotatable element 40. The motorised rotatable element 40 is configured for a tool to be mounted thereto so that the tool may be rotated with respect to the rest of the second segment 14. The rotatable element 40 has a rotatable surface 41 that faces away from a remaining portion of the joint. The motorised rotatable element 40 is driven by a rotatable element motor 42 such that the motorised rotatable element 40 may rotate about a rotatable element axis. The motorised rotatable element 40 is continuously rotatable about the rotatable element axis in a motor element rotational direction about the motorised rotatable element axis and an opposite motor element rotational direction about the motorised rotatable element axis. This enables infinite “roll motion” for a tool mounted to the rotatable element. The rotatable element 40 is preferably directly driven by the rotatable element motor 42. A rotatable element direct drive mechanism mechanically connects the rotatable element motor 42 and the motorised rotatable element 40. The motorised rotatable element direct drive mechanism preferably comprises a rotatable element drive shaft that extends co-directionally with the rotatable element axis (although the rotatable element drive shaft is not shown in Figure 1). The rotatable element motor 42 is located within the internal space 43. The rotatable element motor 42 is preferably directly fixed to the second segment such that it is located within the internal space 43. The internal mounting of the motors 24, 30, 42 means that the joint is far more compact with respect to prior arrangements. The first, second and / or rotatable element motors 24, 30, 42 are preferably electric motors and to provide improved cable management are electrically connected in series. Referring now to Figure 2A (which shows the joint 10 without its internal components), the joint 10 is shown in a neutral position where the first and second segments 12, 14 are positioned opposite one another. As shown, each set of linkages 16, 18, 20, 22 comprises three linkages. In particular each set of linkages comprises an input linkage 50 pivotably connected to the first segment 12, an output linkage 52 pivotably connected to the second segment 14, and an intermediate linkage 54 connecting the input and output linkages 50, 52. The intermediate linkage 54 is pivotably connected to each of the input and output linkages 50, 52. Not all of the input, intermediate and output linkages 50, 54, 52 have been allocated a specific reference numeral in Figure 2 to make Figure 2 easier for the viewer to view. Bearings may be employed to reduce friction between the linkages. In particular, a first pivotable connection between the input linkage 50 and the intermediate linkage 54 may comprise a first bearing (not shown) and a second pivotable connection between the output linkage 52 and intermediate linkage 54 may comprise a second bearing (not shown). As depicted the sets of linkages 16, 18, 20, 22 have substantially the same construction. In particular, the motorised sets of linkages may have substantially the same construction as the non-motorised sets of linkages. As shown, the input linkages 50 of the sets of linkages 16, 18, 20, 22 comprise first and second input linkage pairs 56, 58 of input linkages. Each of the input linkages of the first input linkage pair of input linkages 56 may pivot about a first common input linkage pivot axis b. Each of the input linkages of the second input linkage pair of input linkages 58 may pivot about a second common input linkage pivot axis a. The first common input linkage pivot axis b is orthogonal to the second common input linkage pivot axis a. The first common input linkage pivot axis b is the first axis (i.e., the shaft axis of the rotatable drive shaft 26 of the first direct drive mechanism described in relation to Figure 1). The second common input pivot axis a is the second axis (i.e., the output shaft axis of the output shaft of the second drive mechanism described in relation to Figure 1). A first input linkage distance between each input linkage of the first input linkage pair 56 along the first common input pivot axis b is the same as a second input linkage distance between each input linkage of the second input linkage pair 58 along the second common input pivot axis a. In other words, the spacing between the linkages of the first and second input linkage pairs 56, 58 is the same. The output linkages 52 of the sets of linkages 16, 18, 20, 22 comprise first and second output linkage pairs 60, 62 of output linkages. The first output linkage pair of output linkages 60 may pivot about a first common output linkage pivot axis b’. The second output linkage pair 62 of output linkages may pivot about a second common output linkage pivot axis a’. The first common output linkage pivot axis b’ is orthogonal to the second common output linkage pivot axis a’. The first common output linkage pivot axis b’ and the second common output pivot axis a’ is always orthogonal to the rotational element axis c during movement of the joint. A first output linkage distance between each output linkage of the first output linkage pair 60 along the first common output pivot axis b’ is the same as a second output linkage distance between each output linkage of the second output linkage pair 62 along the second common output pivot axis a’. Referring now to Figure 2B (which shows the same view as Figure 2A with reference numerals relating to different components), the input linkages 50 are pivotably connected to the first segment 12 around a first segment outer circumference of the first segment at first connection points 70. The first connection points 70 are evenly arranged around the first segment outer circumference. In the depicted example, each first connection point 70 is rotationally spaced apart from adjacent first connection points 70 by a first rotational angle of substantially 90 degrees. The first segment outer circumference is preferably a first outer circumference of the first body portion 36. The output linkages are pivotably connected to the second segment 14 around a second segment outer circumference of the second segment at second connection points 72. The second connection points 72 are evenly arranged around the second segment outer circumference. The second segment outer circumference is preferably a second outer circumference of the second body portion 38. As shown for a given set of linkages 16, 18, 20, 22 the first connection point 70 associated with the given set is rotationally offset by a rotational angle of 180 degrees from the second connection point 72 associated with that set (in the neutral position where the first and second segments 12, 14 are positioned opposite one another). As shown, in the neutral position, the first common input pivot axis b is parallel with the first common output pivot axis b’, and the second common input pivot axis a is parallel with the second common output pivot axis a’. In the neutral position, all of the axes a, a’, b, b’ are orthogonal to the rotational element axis c. It should also be noted that the first common input pivot axis b is the first axis about which the first motorised set of linkages 16 pivots and the second common input pivot axis a is the second axis about which the second motorised set of linkages 18 pivots. In the neutral position, centroids of the first and second segments lie on the rotatable element axis c. It should be noted that in the neutral position all the sets of linkages 16, 18, 20, 22 are spaced apart from one another and are in the same configuration. Further, the intermediate linkages 54 in particular are parallel to one another and are evenly spaced from the rotatable element axis c. As shown each of the linkages 16, 18, 20, 22 of each set are curved. The intermediate linkages curve in a different direction to the input and output linkages 50, 52. In the depicted example the intermediate linkages 54 are concave (i.e., they curve inwards towards the rotatable element axis c in the neutral position). By contrast, the input linkages 50 and output linkages 52 are convex and curve outwardly in a direction away from the rotatable element axis c. In other words, in the neutral position, the input and output linkages 50, 52 are concave to the rotatable element axis c. In terms of its specific construction, each linkage is elongate, and comprises two parallelly and longitudinally extending arms 73. The arms 73 extend between heads 74 that are for receiving a pivot or comprise a pivot for inserting into another linkage. Struts 76 extend transversely between the parallelly extending arms. In the neutral position, a first plane comprises the rotatable element axis c and the first common input linkage pivot axis b. In particular, the rotatable element axis c and the first input linkage pivot axis b extend in the first plane. Referring now to Figure 3, where the joint 10 is viewed from a viewing position orthogonal to the first plane in which the first common input linkage axis and rotatable element axis extend. As shown, when the joint 10 is viewed from the viewing position that is orthogonal to the first plane, the input linkage 50 of a viewable set of linkages 18 extends from where it is pivotably connected to the first segment 12 to the intermediate linkage 54 of the viewable set of linkages along an input linkage axis X, and the output linkage 52 of the viewable set of linkages 18 extends from where it is connected to the second segment 14 to the intermediate linkage 54 along an output linkage axis Y. The input linkage axis X and output linkage axis Y intersect each other at an intersection point A. The viewable set of linkages 18 are symmetric to the intersection point A when viewed from the viewing position. In particular, the intersection point A lies in a dividing plane that is orthogonal to the first plane and the viewable set of linkages are symmetric about the dividing plane when viewed from the viewing position. A nonzero angle y is between the input and output axes. The non-zero angle may be an angle in the range of 30 to 80 degrees, preferably 40 to 70 degrees. In particular embodiments, the non-zero angle is 45 degrees. In other embodiments, the non-zero angle is 60 degrees. Having a non-zero angle of 45 degrees is particularly beneficial as it enables a movable joint that has particularly good mobility. As shown, there is a distance d between the pivot axes a, a’ of the second pairs of input and output linkages. Reference is now made to Figure 4, which shows how the movable joint 10 may move between different positions. Due to the specific arrangement of the sets of linkages 16, 18, 20, 22 of the present invention, point A referred to in relation to Figure 3, always lies on a homokinetic plane (P) bisecting centre axes of the first and second segments 12, 14. Torque from the first motor supplied about the first axis b (shown in Fig. 2A) is conveyed to the first common input pivot axis b’ (shown in Fig. 2A) by the sets of linkages and similarly torque supplied about the second axis a (shown in Fig. 2A) by the second motor is conveyed to the second output pivot axis a’ (shown in Fig. 2a) by the sets of linkages, meaning that the joint 10 exhibits homokinetic behaviour. The specific arrangement of sets of linkages 16, 18, 20, 22 enable the first and second segments 12, 14 to move about first and second imaginary spherical surfaces 100, 110. In particular, a second centre axis (CA) of the second segment 14 can deviate from a first centre axis (CF) of the first segment 12 by bend and swing angles 0, q) that lie in different and orthogonal planes. The invention enables a movable joint with 3 degrees of freedom, thereby meaning the joint has improved mobility with respect to prior arrangements, allowing a tool mounted to the joint to move more freely. The present invention also provides a lightweight and compact movable joint where cables can be stored internally within the joint. The movable joint of the present invention is therefore particularly suited for use in an industrial robotic or medical manipulator. The joint of the present invention is also simplified with respect to prior arrangements, making manufacture of the joint easier. The joint provides good weight distribution meaning component parts may be 3D printed or made using simple casting / moulding techniques. Advantageously, the joint of the present invention allows electrical cables to be housed within the joint, making the joint more compact as well as meaning that the joint is more robust as those cables are not likely to break during movement of the joint. Advantageously, the motorised rotatable element enables a tool attached to the second segment to rotate, thereby providing an additional movement option for moving the tool in addition to the corrective roll motion. The daisy chaining of the electrical components of the joint allows for better cable management within the joint. In the prior OW and QJ, a twist motion is observed at the output end (as a result of the combination of bend and swing angles 9, (p), inherent to the mechanics of the 2DoF motion available. The third motor 42 of the present invention (referred to as a rotatable element motor) connected to rotatable surface 41 is used to compensate for this undesirable twist motion and have better control on the observed motion trajectory and poses. The one or more embodiments are described above by way of example only. Many variations are possible without departing from the scope of protection afforded 5 by the appended claims.

Claims

1. A movable joint comprising:a first segment;a second segment; andsets of linkages connecting the first and second segments, the sets of linkages comprising a first motorised set of linkages that is directly driven by a first motor.

2. The joint of claim 1, wherein a first direct drive mechanism mechanically connects the first motor and the first motorised set of linkages.

3. The joint of claim 2, wherein the first direct drive mechanism comprises a first rotatable drive shaft that extends along a first axis, wherein the rotatable drive shaft is directly coupled to the first motorised set of linkages, wherein the first motorised set of linkages pivots about the first axis.

4. The joint of any preceding claim, wherein the sets of linkages comprise a second motorised set of linkages, wherein the second motorised set of linkages is driven by a second motor.

5. The joint of claim 4, wherein the second drive mechanism mechanically connects the second motorised set of linkages and the second motor, wherein the second drive mechanism comprises input and output shafts mechanically connected by gears.

6. The joint of claim 4 or 5, wherein the second motor is mounted on the first motor.

7. The joint of any of claims 4 to 6, wherein the second motorised set of linkages is pivotable about a second axis.

8. The joint of any preceding claim, wherein the second segment comprises a motorised rotatable element.

9. The joint of claim 8, wherein the motorised rotatable element rotates about a rotatable element axis.

10. The joint of claim 8 or 9, wherein the motorised rotatable element is driven by a rotatable element motor.

11. The joint of claim 10, wherein the motorised rotatable element is directly drivenby the rotatable element motor.

12. The joint of any preceding claim, wherein the first motor is internally mounted within the joint.

13. The joint of any preceding claim, wherein the sets of linkages extend from the first segment to the second segment, wherein the first segment comprises a first body portion and the second segment comprises a second body portion, wherein the sets of linkages define with the first and second body portions an internal space within the joint in which the first motor is located.

14. The joint of any preceding claim, wherein the sets of linkages consist of four sets of linkages.

15. The joint of any preceding claim, wherein each set of linkages comprises three linkages.

16. The joint of claim 15, wherein each set of linkages comprises an input linkage pivotably connected to the first segment, an output linkage pivotably connected to the second segment, and an intermediate linkage connecting the input and output linkages, wherein the intermediate linkage is pivotably connected to each of the input and output linkages.

17. The joint of claim 16, wherein the input linkages of the sets of linkages comprisefirst and second input linkage pairs of input linkages, wherein each of the input linkages of the first input linkage pair of input linkages pivots about a first common input linkage pivot axis, wherein each of the input linkages of the second input linkage pair of input linkages pivots about a second common input linkage pivot axis, wherein the first common input linkage pivot axis is orthogonal to the second common input linkage pivot axis.

18. The joint of claim 17, wherein a first input linkage distance between each input linkage of the first input linkage pair along the first common input pivot axis isthe same as a second input linkage distance between each input linkage of the second input linkage pair along the second common input pivot axis.

19. The joint of any of claims 16 to 18, wherein the output linkages of the sets of linkages comprise first and second output linkage pairs of output linkages, wherein the first output linkage pair of output linkages pivots about a first common output linkage pivot axis, wherein the second output linkage pair of output linkages pivots about a second common output linkage pivot axis, wherein the first common output linkage pivot axis is orthogonal to the second common output linkage pivot axis.

20. The joint of claim 19, wherein a first output linkage distance between each output linkage of the first output linkage pair along the first common output pivot axis is the same as a second output linkage distance between each output linkage of the second output linkage pair along the second common output pivot axis.

21. The joint of any of claims 16 to 20, wherein the input linkages are pivotably connected to the first segment around a first segment outer circumference of the first segment.

22. The joint of any of claims 16 to 21, wherein the output linkages are pivotably connected to the second segment around a second segment outer circumference of the second segment.

23. The joint of any of claims 16 to 22, wherein in a neutral position, the first and second segments are positioned opposite one another, wherein in the neutral position, the intermediate linkages of the sets of linkages are substantially parallel to one another.

24. The joint of claim 23, wherein in the neutral position, each set of linkages has the same configuration.

25. A robotic apparatus comprising:the movable joint of any preceding claim; anda tool mounted on the second segment.

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