it is known to use robots for assisting and performing surgery. Figure 1 illustrates a typical surgical robot 100 which consists of a base 108, an arm 102, and an instrument 105. The base supports the robot, and is itself attached rigidly to, for example, the operating theatre floor, the operating theatre ceiling or a trolley. The arm extends between the base and the instrument. The arm is articulated by means of multiple flexible joints 103 along its length, which are used to locate the surgical instrument in a desired location relative to the patient. The surgical instrument is attached to the distal end 104 of the robot arm. The surgical instrument penetrates the body of the patient 101 at a port 107 so as to access the surgical site. At its distal end, the instrument comprises an end effector 106 for engaging in a medical procedure.

Figure 2 illustrates a typical surgical instrument 200 for performing robotic laparoscopic surgery. The surgical instrument comprises a base 201 by means of which the surgical instrument connects to the robot arm. A shaft 202 extends between base 201 and articulation 203. Articulation 203 terminates in an end effector 204. In figure 2, a pair of serrated jaws are illustrated as the end effector 204. The articulation 203 permits the end effector 204 to move relative to the shaft 202. It is desirable for at least two degrees of freedom to be provided to the motion of the end effector 204 by means of the articulation.

Figure 3 illustrates an example of a known surgical instrument 300 in which end effector 204 is permitted to move relative to shaft 202 by means of pitch joint 301 and two yaw joints 302. Joint 301 enables the end effector 204 to rotate about pitch axis 303. Joints 302 enable each jaw of the end effector 204 to rotate about yaw axis 304. The joints are driven by cables 306, 307 and 308. Pulley 305 is used to direct cables 307 and 308 from their passage over the pitch joint to the yaw joints. Pulley 305 is offset from the central axis of the articulation 203. The external diameter of the shaft is 8mm in order to accommodate the number, size and location of the internal elements of the articulated portion.

It is desirable to reduce the external diameter of the instrument in order to minimise the size of the incision through the skin of the patient and minimise disruption inside the patient's body. It is also desirable to minimise the weight of the surgical instrument so as to minimise the size and weight of the robot base a nd arm required to support the instrument, thereby enabling the robot as a whole to be more compact and hence occupy a sma ller space in the operating theatre and be more moveable within the operating theatre.

I n a typical laparoscopy operation, a surgeon utilises many instruments, and hence exchanges one instrument for another many times. It is therefore desirable to minimise the time taken and maximise the ease with which one instrument is detached from a robot arm and a different instrument is attached. Additionally, it is desirable to minimise the time taken in setting up the instrument ready for use once it has been attached to the robot arm.

SUMMARY OF THE I NVENTION

According to an aspect of the invention, there is provided a robotic surgical instrument as set out in the accompanying claims.

BRI EF DESCRI PTION OF THE FIGURES

The present invention will now be described by way of example with reference to the accompanying drawings. I n the drawings:

Figure 1 illustrates a surgical robot performing a surgical procedure;

Figure 2 illustrates a known surgical instrument;

Figure 3 illustrates a known arrangement of an articulated end effector of a surgical instrument;

Figure 4 illustrates a surgical robot;

Figures 5a and 5b illustrate a distal end of a surgical instrument;

Figures 6a and 6b illustrate a pulley arrangement of the distal end of the surgical instrument of figures 5a and 5b in a straight configuration;

Figure 7 illustrates a pulley arrangement of the distal end of the surgical instrument of figures 5a and 5b in a variety of non-straight configurations;

Figure 8 illustrates the offset pulleys of the pulley arrangement shown in figures 5a and 5b;

Figure 9 illustrates non-straight configurations of the distal end of a surgical instrument;

Figure 10 illustrates a supporting body and redirecting pulleys of the articulation of a surgical instrument;

Figure 11 illustrates a different view of the supporting body and redirecting pulleys of figure 10;

Figures 12 and 13 illustrate the supporting body of the articulation of figures 10 and

11 in isolation;

Figure 14 illustrates a spindle mounted redirecting pulley mounted to the supporting body of figures 12 and 13;

Figure 15 illustrates a bevelled surface and groove of the supporting body of figures

12 and 13;

Figure 16 illustrates arrangements of driving elements in an instrument shaft;

Figures 17a and 17b illustrate two views of a surgical instrument;

Figure 18 illustrates spokes in an instrument shaft;

Figures 19a, 19b and 19c illustrate three views of an instrument interface;

Figures 20a and 20b illustrate tensioning mechanisms;

Figures 21a, 21b and 21c illustrate three views of a drive assembly interface of a robot arm;

Figures 22a, 22b and 22c illustrate configurations of an instrument interface element; Figure 23 illustrates a configuration of a drive assembly interface element;

Figure 24 illustrates an instrument interface engaged in a drive assembly interface; and

Figure 25 illustrates a further view of an instrument interface.

DETAILED DESCRIPTION

Figure 4 illustrates a surgical robot having an arm 400 which extends from a base 401. The arm comprises a number of rigid limbs 402. The limbs are coupled by revolute joints 403. The most proximal limb 402a is coupled to the base by joint 403a. It and the other limbs are coupled in series by further ones of the joints 403. Suitably, a wrist 404 is made up of four individual revolute joints. The wrist 404 couples one limb (402b) to the most distal limb (402c) of the arm. The most distal limb 402c carries an attachment 405 for a surgical instrument 406. Each joint 403 of the arm has one or more motors 407 which can be operated to cause rotational motion at the respective joint, and one or more position and/or torque sensors 408 which provide information regarding the current configuration and/or load at that joint. Suitably, the motors are arranged proximally of the joints whose motion they drive, so as to improve weight distribution. For clarity, only some of the motors and sensors are shown in figure 4. The arm may be generally as described in our co-pending patent application PCT/GB2014/053523.

The arm terminates in an attachment 405 for interfacing with the instrument 406. Suitably, the instrument 406 takes the form described with respect to figure 2. The instrument has a diameter less than 8mm. Suitably, the instrument has a 5mm diameter. The instrument may have a diameter which is less than 5mm. The instrument diameter may be the diameter of the shaft. The instrument diameter may be the diameter of the profile of the articulation. Suitably, the diameter of the profile of the articulation matches or is narrower than the diameter of the shaft. The attachment 405 comprises a drive assembly for driving articulation of the instrument. Movable interface elements of the drive assembly interface mechanically engage corresponding movable interface elements of the instrument interface in order to transfer drive from the robot arm to the instrument. One instrument is exchanged for another several times during a typical operation. Thus, the instrument is attachable and detachable from the robot arm during the operation. Features of the drive assembly interface and the instrument interface aid their alignment when brought into engagement with each other, so as to reduce the accuracy with which they need to be aligned by the user.

The instrument 406 comprises an end effector for performing an operation. The end effector may take any suitable form. For example, the end effector may be smooth jaws, serrated

jaws, a gripper, a pair of shears, a needle for suturing, a camera, a laser, a knife, a stapler, a cauteriser, a suctioner. As described with respect to figure 2, the instrument comprises an articulation between the instrument shaft and the end effector. The articulation comprises several joints which permit the end effector to move relative to the shaft of the instrument. The joints in the articulation are actuated by driving elements, such as cables. These driving elements are secured at the other end of the instrument shaft to the interface elements of the instrument interface. Thus, the robot arm transfers drive to the end effector as follows: movement of a drive assembly interface element moves an instrument interface element which moves a driving element which moves a joint of the articulation which moves the end effector.

Controllers for the motors, torque sensors and encoders are distributed with the robot arm. The controllers are connected via a communication bus to control unit 409. A control unit 409 comprises a processor 410 and a memory 411. Memory 411 stores in a non-transient way software that is executable by the processor to control the operation of the motors 407 to cause the arm 400 to operate in the manner described herein. In particular, the software can control the processor 410 to cause the motors (for example via distributed controllers) to drive in dependence on inputs from the sensors 408 and from a surgeon command interface 412. The control unit 409 is coupled to the motors 407 for driving them in accordance with outputs generated by execution of the software. The control unit 409 is coupled to the sensors 408 for receiving sensed input from the sensors, and to the command interface 412 for receiving input from it. The respective couplings may, for example, each be electrical or optical cables, or may be provided by a wireless connection. The command interface 412 comprises one or more input devices whereby a user can request motion of the end effector in a desired way. The input devices could, for example, be manually operable mechanical input devices such as control handles or joysticks, or contactless input devices such as optical gesture sensors. The software stored in memory 411 is configured to respond to those inputs and cause the joints of the arm and instrument to move accordingly, in compliance with a pre-determined control strategy. The control strategy may include safety features which moderate the motion of the arm and instrument in response to command inputs. Thus, in summary, a surgeon at the command interface 412 can control the instrument 406 to move

in such a way as to perform a desired surgical procedure. The control unit 409 and/or the command interface 412 may be remote from the arm 400.

Figures 5a and 5b illustrate opposing views of the distal end of a surgical instrument. In figures 5a and 5b, the end effector 501 comprises a pair of end effector elements 502, 503, which in figures 5a and 5b are depicted as a pair of opposing serrated jaws. It will be understood that this is for illustrative purposes only. The end effector may take any suitably form, such as those described above. The end effector 501 is connected to the shaft 504 by articulation 505. Articulation 505 comprises joints which permit the end effector 501 to move relative to the shaft 504. A first joint 506 permits the end effector 501 to rotate about a first axis 510. The first axis 510 is transverse to the longitudinal axis of the shaft 511. A second joint 507 permits the first end effector element 502 to rotate about a second axis 512. The second axis 512 is transverse to the first axis 510. A third joint 513 permits the second end effector element 503 to rotate about the second axis 512. Suitably, the first end effector element 502 and the second end effector element 503 are independently rotatable about the second axis 512 by the second and third joints. The end effector elements may be rotated in the same direction or different directions by the second and third joints. The first end effector element 502 may be rotated about the second axis, whilst the second end effector element 503 is not rotated about the second axis. The second end effector element 503 may be rotated about the second axis, whilst the first end effector element 502 not rotated about the second axis.

Figures 5a and 5b depict a straight configuration of the surgical instrument in which the end effector is aligned with the shaft. In this orientation, the longitudinal axis of the shaft 511 is coincident with the longitudinal axis of the articulation and the longitudinal axis of the end effector. Articulation of the first, second and third joints enables the end effector to take a range of attitudes relative to the shaft. Figure 9 illustrates some of the configurations of the distal end of the instrument in which articulation about all the first, second and third joints has been driven relative to the straight configuration of figures 5a and 5b.

Returning to figures 5a and 5b, the shaft terminates at its distal end in the first joint 506. The articulation 505 comprises a supporting body 509. At one end, the supporting body 509 is connected to the shaft 504 by the first joint 506. At its other end, the supporting body 509 is connected to the end effector 501 by second joint 507 and third joint 513. Thus, first joint 506 permits the supporting body 509 to rotate relative to the shaft 504 about the first axis 510; and the second joint 507 and third joint 513 permit the end effector elements 502, 503 to rotate relative to the supporting body 509 about the second axis 512.

In the figures, the second joint 507 and third joint 513 both permit rotation about the same axis 512. However, the second and third joints may alternatively permit rotation of the end effector elements about different axes. The axis of rotation of one of the end effector elements may be offset in the longitudinal direction of the shaft 504 from the axis of rotation of the other end effector element. The axis of rotation of one of the end effector elements may be offset in a direction transverse to the longitudinal direction of the shaft 504 from the axis of rotation of the other end effector element. The axis of rotation of one of the end effector elements may not be parallel to the axis of rotation of the other end effector element. The axes of rotation of the end effector elements 502, 503 may be offset in the longitudinal direction of the shaft and/or offset in a direction perpendicular to the longitudinal direction of the shaft and/or angled with respect to each other. This may be desirable as a result of the end effector elements being asymmetric. For example, in an electrosurgical element, a first end effector element may be powered and a second end effector element not powered and insulated from the first end effector element. To aid this, the axes of rotation of the two end effector elements may be offset in the direction perpendicular to the longitudinal direction of the shaft. In another example, a first end effector element may be a blade and a second end effector element a flat cutting surface. To aid use of the blade, the axes of rotation of the two end effector elements may be angled to one another.

The joints of the articulation are driven by driving elements. The driving elements are elongate elements which extend from the joints in the articulation through the shaft to the instrument interface. Suitably, each driving element can be flexed laterally to its main extent at least in those regions where it engages the internal components of the articulation and instrument interface. In other words, each driving element can be flexed transverse to its longitudinal axis in the specified regions. This flexibility enables the driving elements to wrap around the internal structure of the instrument, such as the joints and pulleys. The driving elements may be wholly flexible transverse to their longitudinal axes. The driving elements are not flexible along their main extents. The driving elements resist compression and tension forces applied along their length. In other words, the driving elements resist compression and tension forces acting in the direction of their longitudinal axes. The driving elements have a high modulus. The driving elements remain taut in operation. They are not permitted to become slack. Thus, the driving elements are able to transfer drive from the instrument interface to the joints. The driving elements may be cables.

Suitably, each joint is driven by a pair of driving elements. Referring to figures 5a and 5b, the first joint 506 is driven by a first pair of driving elements A1,A2. The second joint 507 is driven by a second pair of driving elements B1,B2. The third joint is driven by a third pair of driving elements C1,C2. Suitably, each joint is driven by its own pair of driving elements. In other words, each joint is driven by a dedicated pair of driving elements. Suitably, the joints are independently driven. A pair of driving elements may be constructed as a single piece as shown for the third pair of driving elements in figures 5a and 5b. In this case, the single piece is secured to the joint at one point. For example, the third pair of driving elements C1,C2 comprises a ball feature 520 which is secured to the third joint 513. This ensures that when the pair of driving elements is driven, the drive is transferred to motion of the joint about its axis. Alternatively, a pair of driving elements may be constructed as two pieces. In this case, each separate piece is secured to the joint.

The surgical instrument of figures 5a and 5b further comprises a pulley arrangement around which the second and third pairs of driving elements are constrained to move. The pulley arrangement is better illustrated in figures 6a and 6b. The supporting body 509 is not shown in figures 6a and 6b in order to more clearly illustrate the pulley arrangement. The pulley arrangement comprises a first set of pulleys 601. The first set of pulleys 601 is rotatable about the first axis 510. Thus, the first set of pulleys 601 rotate about the same axis as the first joint 506. The pulley arrangement further comprises a second set of pulleys 602. The pulley arrangement further comprises a pair of redirecting pulleys 603.

The pulley arrangement is more clearly illustrated in figure 7. The supporting body, the first joint and the first pair of driving elements have all been omitted from figure 7 in order to

more clearly illustrate the pulley arrangement. The second set of pulleys comprises a first pulley 701 and a second pulley 702. The first pulley 701 is rotatable about a third axis 703 which is parallel to the first axis 510. The third axis 703 is offset from the first axis 510 both in the longitudinal direction of the shaft and also transverse to the longitudinal direction of the shaft. The second pulley 702 is rotatable about a fourth axis 704 which is parallel to the first axis 510. The fourth axis 704 is offset from the first axis 510 both in the longitudinal direction of the shaft and also transverse to the longitudinal direction of the shaft. The third and fourth axes are parallel but offset from each other. The third axis 703 and fourth axis 704 are in the same plane perpendicular to the longitudinal direction of the shaft. Figure 8 illustrates the distal end of the surgical instrument from a different view which more clearly shows the offset axes of the first pulley 701 and the second pulley 702 of the second set of pulleys. By offsetting the first pulley 701 and the second pulley 702, the driving element wrapped around each pulley is able to extend down the shaft after having wrapped around the pulley. As shown in figure 6a, the first pulley 701 and second pulley 702 of the second set of pulleys 602 are located on opposing sides of the first joint 506 in a longitudinal direction of the shaft 504. The first pulley 701 and second pulley 702 are located on opposing sides of the first pair of driving elements A1,A2.

The second set of pulleys is located between the first set of pulleys and the instrument interface end of the shaft. Suitably, the second set of pulleys is located within the shaft as shown in the figures. Alternatively, the second set of pulleys may be located within the articulation between the first joint 506 and the second joint 507. However, by locating the second set of pulleys at the distal end of the shaft 508, the distance between the first and second joints is reduced compared to the alternative arrangement in which the second set of pulleys are located in the articulation, thereby reducing the stiffness of the supporting body 509 required to maintain accurate positioning of the end effector 501.

The first set of pulleys 601 comprises a first pulley 705 and a second pulley 706. Both the first pulley 705 and the second pulley 706 rotate about the first axis 510. The first pulley 705 and the second pulley 706 of the first set of pulleys are located on opposing sides of the first joint 506 in a longitudinal direction of the shaft 504. The first pulley 705 and the second pulley 06 are located on opposing ends of the first axis 510. The first pulley 705 and the second pulley 706 are located on opposing sides of the first pair of driving elements A1,A2.

The second pair of driving elements B1,B2 is constrained to move around opposing sides of the first pulley 705 and the second pulley 706 of the first set of pulleys 601. The second pair of driving elements B1,B2 is constrained to move around opposing sides of the first pulley 701 and the second pulley 702 of the second set of pulleys 601. The second pair of driving elements is constrained to move around opposing sides of the first pulley 705 of the first set of pulleys 601 and the first pulley 701 of the second set of pulleys 602. The second pair of driving elements is constrained to move around opposing sides of the second pulley 706 of the first set of pulleys 601 and the second pulley 702 of the second set of pulleys 602.

The third pair of driving elements C1,C2 is constrained to move around opposing sides of the first pulley 705 and the second pulley 706 of the first set of pulleys 601. The third pair of driving elements C1,C2 is constrained to move around opposing sides of the first pulley 701 and the second pulley 702 of the second set of pulleys 601. The third pair of driving elements is constrained to move around opposing sides of the first pulley 705 of the first set of pulleys 601 and the first pulley 701 of the second set of pulleys 602. The third pair of driving elements is constrained to move around opposing sides of the second pulley 706 of the first set of pulleys 601 and the second pulley 702 of the second set of pulleys 602.

The second and third pairs of driving elements are each constrained to extend over the first joint 506 in order to reach the second and third joints respectively. Thus, the first one of the second pair of driving elements Bl passes over one side of the first pulley 705 of the first set of pulleys on the first joint axis 510, and the second one of the second pair of driving elements B2 passes over an opposing side of the second pulley 706 of the first set of pulleys on the first joint axis 510, so that whatever rotation there is of the supporting body 509 about the first joint 506, the length of the second pair of driving elements B1,B2 is maintained the same. Similarly, the first one of the third pair of driving elements CI passes over one side of the second pulley 706 of the first set of pulleys on the first joint axis 510, and the second one of the third pair of driving elements C2 passes over an opposing side of the first pulley 705 of the first set of pulleys on the first joint axis 510, so that whatever rotation there is of the supporting body 509 about the first joint 506, the length of the third pair of driving elements C1,C2 is maintained the same. If the arrangement of the instrument interface is symmetric for both the second pair of driving elements B1,B2 and the third pair of driving elements C1,C2, then the length of the second pair of driving elements is the same as the length of the third pair of driving elements for all rotation angles of the supporting body 509 about the first joint 506. In every configuration of the surgical instrument, the second pair of driving elements and the third pair of driving elements remain taut. They are never slack. Thus, there is no backlash when articulating any of the joints of the surgical instrument. Thus, full control of all three degrees of freedom of movement of the surgical instrument is achieved in every configuration of the surgical instrument.

Suitably, each pulley of the first set of pulleys 601 comprises a pair of pulley elements. The first pulley 705 comprises an inside pulley element 708 and an outside pulley element 709. Inside pulley element 708 is located between the outside pulley element 709 and the first pair of driving elements A1,A2. Suitably, inside pulley element 708 abuts outside pulley element 709. The inside pulley element 708 may be fast with the outside pulley element 709. The inside pulley element 708 may be integrally formed with the outside pulley element 709. The second pulley 706 comprises an inside pulley element 710 and an outside pulley element 711. Inside pulley element 710 is located between the outside pulley element 711 and the first pair of driving element A1,A2. Suitably, inside pulley element 710 abuts outside pulley element 711. The inside pulley element 710 may be fast with the outside pulley element 711. The inside pulley element 710 may be integrally formed with the outside pulley element 711. Each pulley element comprises a groove for seating a driving element.

Suitably, each pulley of the second set of pulleys 602 comprises a pair of pulley elements. The first pulley 701 comprises an inside pulley element 712 and an outside pulley element 713. Inside pulley element 712 is located between the outside pulley element 713 and the first pair of driving elements A1,A2. Suitably, inside pulley element 712 abuts outside pulley element 713. The inside pulley element 712 may be fast with the outside pulley element 713. The inside pulley element 712 may be integrally formed with the outside pulley element 713. The second pulley 702 comprises an inside pulley element 714 and an outside pulley element 715. Inside pulley element 714 is located between the outside pulley element 715 and the first pair of driving element A1,A2. Suitably, inside pulley element 714 abuts outside pulley element 715. The inside pulley element 714 may be fast with the outside pulley element 715. The inside pulley element 714 may be integrally formed with the outside pulley element 715. Each pulley element comprises a groove for seating a driving element.

The second pair of driving elements B1,B2 is constrained to move around the inside pulley element 712 of the first pulley of the second set of pulleys and the outside pulley element 715 of the second pulley of the second set of pulleys. The second pair of driving elements Bl, B2 is constrained to move around the inside pulley element 708 of the first pulley of the first set of pulleys and the outside pulley element 711 of the second pulley of the first set of pulleys.

The third pair of driving elements C1,C2 is constrained to move around the outside pulley element 713 of the first pulley of the second set of pulleys and the inside pulley element 714 of the second pulley of the second set of pulleys. The third pair of driving elements C1,C2 is constrained to move around the outside pulley element 709 of the first pulley of the first set of pulleys and the inside pulley element 710 of the second pulley of the first set of pulleys.

Thus, the second pair of driving elements B1,B2 has a symmetrically opposing path around the first and second sets of pulleys 601, 602 than the third pair of driving elements C1,C2. In the straight configuration of the instrument in which the end effector is aligned with the shaft, the path of the second pair of driving elements B1,B2 about the pulley arrangement is rotationally symmetrical about the longitudinal axis of the shaft 511 to the path of the third pair of driving elements C1,C2 about the pulley arrangement. The second and third pairs of driving elements B1,B2 and C1,C2 emerge from the second set of pulleys 602 into the distal end of the shaft in a symmetrical arrangement. As can be more easily seen on figure 7, the driving elements Bl and C2 emerge adjacent to each other on one side of the shaft, and the driving elements CI and B2 emerge adjacent to each other on an opposing side of the shaft. The arrangement of driving elements Bl and C2 in the shaft is rotationally symmetrical to the arrangement of driving elements CI and B2 in the shaft, about the longitudinal axis of the shaft 511. The second set of pulleys 602 redirects the second and third pairs of driving elements from the first set of pulleys 601 into the shaft in this manner.

Figure 7 illustrates the distal end of the surgical instrument in five different configurations. Configuration (c) is the straight configuration previously mentioned, in which the end effector is aligned with the instrument shaft. In configurations (a), (b), (d) and (e), rotation about the first joint has occurred relative to configuration (c). In configurations (a), (b), (d) and (e), no rotation about either the second or third joint has occurred relative to configuration (c). Starting from configuration (c), the driving element A2 (not shown) is pulled in order to cause the rotation about the first axis 510 leading to the arrangement of configuration (b). The driving element A2 is further pulled to cause further rotation about the first axis 510 to lead to the arrangement of configuration (a). Starting from configuration (c), the driving element Al (not shown) is pulled in order to cause rotation about the first axis 510 in an opposing direction to that in configurations (a) and (b), thereby leading to the arrangement of configuration (d). The driving element Al is further pulled to cause further rotation about the first axis 510 to lead to the arrangement of configuration (e).

Rotation of the end effector 501 about the first axis 510 is bounded by the maximum travel of the first pair of driving elements A1,A2 about the first joint 506. Configuration (a) shows the end effector 501 at maximum rotation about the first axis 510 in one direction, and configuration (e) shows the end effector 501 at maximum rotation about the first axis 510 in the opposing direction. The maximum rotation angle relative to the longitudinal axis of the shaft 511 in both configurations is the angle φ. The second set of pulleys 602 are located relative to the first set of pulleys 601 so as to ensure that the second and third pairs of driving elements are retained in contact with both the first set of pulleys 601 and the second set of pulleys 602 even at the maximum rotation angle φ. For all rotation angles of the end effector 501 about the first axis 510, the end effector 501 always lies within the cone defined by the tangential line connecting the first pulley 701 of the second set of pulleys and the first pulley 705 of the first set of pulleys. That tangential line is the path taken by the driving element. The end effector 501 lies in this cone when the second and third joints are retained in the straight configurations of figures 5a and 5b, as shown in all the configurations of figure 7. As can be seen from figure 7, without the second set of pulleys 602, the driving elements B2 and CI would lose contact with the first set of pulleys 601 in configuration (a). Without the second set of pulleys 602, the driving elements Bl and C2 would lose contact with the first set of pulleys 601 in configuration (e).

The second and third pairs of driving elements are retained in contact with the first and second sets of pulleys for all rotation angles of the end effector relative to the longitudinal axis of the shaft. Thus, regardless of the rotation about the first joint 506, the length of the second pair of driving elements B1,B2 will be maintained the same. Also, regardless of the rotation about the first joint 506, the length of the third pair of driving elements C1,C2 will be maintained the same. Thus, the second set of pulleys enable tension to be retained in the second and third driving elements regardless of how the first joint 506 is driven about the first axis 510. Thus, control of the second and third driving elements is retained regardless of how the first joint 506 is driven about the first axis 510.

The pulley arrangement further comprises a pair of redirecting pulleys 716,717. These redirecting pulleys are in the articulation 505 between the first joint 506 and the second and third joints 507, 513. The redirecting pulleys are positioned so as to redirect the second pair of driving elements B1,B2 from the first set of pulleys 601 to the second joint 507 and to redirect the third pair of driving elements C1,C2 from the first set of pulleys 601 to the third joint 513.

The second pair of driving elements B1,B2 is constrained to move around the first redirecting pulley 716. The first redirecting pulley 716 rotates about a first redirecting pulley axis 718. The first redirecting pulley axis 718 is at an angle 0 to the first axis 510. The angle 0 is such that the first one of the second pair of driving elements Bl is redirected from a take-off point of the first pulley 705 of the first set of pulleys 601 to a pick-up point 721 on the second joint 507. Suitably, the first redirecting pulley 716 comprises a groove which seats the driving element Bl. The third pair of driving elements C1,C2 is not constrained to move around the first redirecting pulley 716. However, the second one of the third pair of driving elements C2 does pass by the first redirecting pulley 716 between its take-off point of the third joint 513 and its pick-up point on the first pulley 705 of the first set of pulleys 601. The driving element C2 may be partially enclosed by the first redirecting pulley 716. For example, the driving

element C2 may partially pass between the wings of the groove of the first redirecting pulley 716, but the driving element C2 is not seated in the groove of the first redirecting pulley 716.

The third pair of driving elements C1,C2 is constrained to move around the second redirecting pulley 717. The second redirecting pulley 717 rotates about a second redirecting pulley axis 719. The second redirecting pulley axis 719 is at an angle ψ to the first axis 510. The angle ψ is such that the first one of the third pair of driving elements CI is redirected from a take-off point 720 of the second pulley 706 of the first set of pulleys 601 to a pick-up point on the third joint 513. Suitably, the second redirecting pulley 717 comprises a groove which seats the driving element CI. The second pair of driving elements B1,B2 is not constrained to move around the second redirecting pulley 717. However, the second one of the second pair of driving elements B2 does pass by the second redirecting pulley 717 between its take-off point 720 of the second joint 507 and its pick-up point on the second pulley 706 of the first set of pulleys 601. The driving element B2 may be partially enclosed by the second redirecting pulley 717. For example, the driving element B2 may partially pass between the wings of the groove of the second redirecting pulley 717, but the driving element B2 is not seated in the groove of the second redirecting pulley 717.

A take-off point is the point at which a driving element loses contact with a pulley. A pick-up point is the point at which a driving element first contacts a pulley. For a driving element passing directly from a first pulley to a second pulley, the take-off point of the driving element from the first pulley and the pick-up point of the driving element on the second pulley are points on a line which is tangential to both the first pulley and the second pulley, the take-off point being where that tangential line intersects the first pulley, and the pick-up point being where that tangential line intersects the second pulley. This is for the purposes of explanation only and treats as negligible the thickness of the driving element. Thus, in reality, the tangential line has a thickness equal to the thickness of the driving element, with the take-off point being where one side of the tangential line meets the first pulley, and the pick-up point being where the other side of the tangential line meets the second pulley.

The redirecting pulley 716 causes the driving element Bl to wrap more fully around the second joint 507 than would happen if the redirecting pulley 716 was not there, thereby

increasing the length of engagement between the driving element Bl and the second joint 507. Thus, the driving element Bl has a greater travel around the second joint 507, and is hence able to cause a larger rotation of the end effector element 502 about the second axis 512 than would be possible without the redirecting pulley 716. The redirecting pulley 716 causes the pick-up point of the driving element Bl on the second joint 507 to change relative to where it would have been without the redirecting pulley 716.

The redirecting pulley 717 causes the driving element CI to wrap more fully around the third joint 513 than would happen if the redirecting pulley 717 was not there, thereby increasing the length of engagement between the driving element CI and the third joint 513. Thus, the driving element CI has a greater travel around the third joint 513, and is hence able to cause a larger rotation of the end effector element 503 about the second axis 512 than would be possible without the redirecting pulley 717. The redirecting pulley 717 causes the pick-up point of the driving element CI on the third joint 513 to change relative to where it would have been without the redirecting pulley 717.

The redirecting pulleys are each located towards the outside edge of the articulation, on opposing sides of the articulation. This is more easily seen on figure 5a. As seen in figure 6a, each redirecting pulley is located between the longitudinal axis of the articulation and the external profile of the articulation, on opposing sides of the articulation. Suitably, the diameter of each redirecting pulley is maximised for the space available. In other words, the redirecting pulley is as large as possible, whilst enabling one driving element to engage the pulley on one side of the pulley and another driving element to pass next to the pulley on the opposing side of the pulley without snagging, the pulley and the two driving elements being encapsulated within the profile of the articulation.

The first redirecting pulley 716 is located in a plane defined by the following three points: (i) the desired take-off point of driving element Bl from the first pulley 705 of the first set of pulleys 601, (ii) the desired pick-up point of driving element Bl on the second joint 507, and (iii) a point on the boundary of the articulation, the point being such that the first redirecting pulley 716 is encapsulated within the boundary of the articulation when located in the plane. Suitably, the first redirecting pulley 716 is as large as possible whilst still being located in this plane, encapsulated within the profile of the articulation, not impeding the path of the driving element C2, and enabling driving element Bl to freely move around it.

The second redirecting pulley 717 is located in a plane defined by the following three points: (i) the desired take-off point of driving element CI from the second pulley 706 of the first set of pulleys 601, (ii) the desired pick-up point of driving element CI on the third joint 513, and (iii) a point on the boundary of the articulation, the point being such that the second redirecting pulley 717 is encapsulated within the boundary of the articulation when located in the plane. Suitably, the second redirecting pulley 717 is as large as possible whilst still being located in this plane, encapsulated within the profile of the articulation, not impeding the path of the driving element B2, and enabling driving element CI to freely move around it.

The desired take-off points and pick-up points are determined so as to allow the desired travel of the driving elements around the second and third joints so as to allow the desired maximum rotation of the end effector elements about the second axis.

The first and second redirecting pulleys are located in different planes. As can be seen in figure 6a, those planes may be symmetrical about a plane which is perpendicular to the first axis 510. Those planes may be rotationally symmetrical about a plane which is perpendicular to the first axis 510. Specifically, those planes may be rotationally symmetrical about a line in a plane which is perpendicular to the first axis 510. When the instrument is in the straight configuration illustrated in figure 6a, those planes are rotationally symmetrical about the longitudinal axis of the shaft 511. This is second order rotational symmetry. Those planes may be a reflection of each other in the plane which is perpendicular to the first axis 510. In the example illustrated, the end effector elements 502 and 503 are rotationally symmetrical, and the paths of the driving elements about the joints 507 and 513 are rotationally symmetrical. Alternatively, the axes of the end effector elements 502 and 503 may be rotationally asymmetrical and/or the paths of the driving elements about the joints 507 and 513 may be asymmetrical. The paths of the driving elements about the joints 507 and 513 may be asymmetrical as a result of the joints having different diameters (to enable different tension ratios) and/or being positioned at different offsets from the centreline of the supporting body 509. In any of these alternative examples, the first and second redirecting

pulleys 716 and 717 would not be rotationally symmetric. They would have different sizes and/or different positions in order to cause the driving elements to have the desired take-off points and pick-up points as previously described.

Suitably, the whole pulley arrangement comprising the first set of pulleys, the second set of pulleys and the redirecting pulleys is symmetrical about a plane which is perpendicular to the first axis 510. Specifically, a first partial arrangement comprising the first pulley of the first set of pulleys 705, the first pulley of the second set of pulleys 701, and the first redirecting pulley 716 is rotationally symmetrical to a second partial arrangement comprising the second pulley of the first set of pulleys 706, the second pulley of the second set of pulleys 702, and the second redirecting pulley 717 about a plane which is perpendicular to the first axis 510. Suitably, the first partial arrangement is a reflection of the second partial arrangement in the mentioned plane which is perpendicular to the first axis 510. The second pair of driving elements B1,B2 is constrained to move around the pulley arrangement in a rotationally symmetrically opposing manner to that in which the third pair of driving elements C1,C2 is constrained to move around the pulley arrangement. Since the pulley arrangement has the described symmetry, the second and third driving elements that are constrained to move symmetrically around the pulley arrangement also have the same symmetry. Thus, the path of the second pair of driving elements B1,B2 about the pulley arrangement is rotationally symmetrical to the path of the third pair of driving elements C1,C2 about the pulley arrangement.

In an exemplary implementation, the first and second redirecting pulleys are mounted on the supporting body 509. Figure 10 illustrates the supporting body 509 and the redirecting pulleys in isolation. Each redirecting pulley is mounted to a surface of the supporting body 509 by a spindle. The spindle 1001 secures the first redirecting pulley 716 to the supporting body 509. A spindle 1102 also secures the second redirecting pulley 717 to the supporting body 509.

As is more clearly illustrated in the view shown in figure 11, the supporting body 509 has a bevelled surface 1101 onto which the first redirecting pulley 716 is mounted. The first redirecting pulley 716 has a mounting surface 1104 which faces the bevelled surface 1101 of the supporting body 509. The mounting surface 1104 is flush with the bevelled surface 1101.

The first redirecting pulley has an opposing surface 1105 which opposes the mounting surface 1104. The opposing surface 1105 is parallel to the mounting surface 1104. The supporting body 509 has a further bevelled surface onto which the second redirecting pulley 717 is mounted by spindle 1103. The second redirecting pulley 717 has a mounting surface 1106 which faces the bevelled surface 1102 of the supporting body 509. The mounting surface 1106 is flush with the bevelled surface 1102. The second redirecting pulley has an opposing surface 1107 which opposes the mounting surface 1102. The opposing surface 1107 is parallel to the mounting surface 1102.

The bevelled surfaces of the supporting body 509 are not parallel to the longitudinal axis of the supporting body. The bevelled surface 1101 of the supporting body 509 is located in a plane 1108 parallel to the plane 1109 in which the first redirecting pulley 716 is located. In other words, the bevelled surface 1101 is located in a plane 1108 parallel to the plane 1109 defined by the following three points: (i) the desired take-off point of driving element Bl from the first pulley 705 of the first set of pulleys 601, (ii) the desired pick-up point of driving element Bl on the second joint 507, and (iii) a point on the boundary of the articulation, the point being such that the first redirecting pulley 716 is encapsulated within the boundary of the articulation when located in the plane 1109. The plane 1108 of the bevelled surface 1101 is offset from the plane 1109 defined by these points by half the width of the first redirecting pulley 716, illustrated as di in figure 11.

The bevelled surface 1102 of the supporting body 509 is located in a plane 1110 parallel to the plane 1111 in which the second redirecting pulley 717 is located. In other words, the bevelled surface 1102 is located in a plane 1110 parallel to the plane 1111 defined by the following three points: (i) the desired take-off point of driving element CI from the second pulley 706 of the first set of pulleys 601, (ii) the desired pick-up point of driving element CI on the third joint 513, and (iii) a point on the boundary of the articulation, the point being such that the second redirecting pulley 717 is encapsulated within the boundary of the articulation when located in the plane 1111. The plane 1110 of the bevelled surface 1101 is offset from the plane 1111 defined by these points by half the width of the second redirecting pulley 717, illustrated as d2 in figure 11. Suitably, the first redirecting pulley 716 and the second redirecting pulley 717 are the same shape and size. In this case, di = d2.

As discussed above, each redirecting pulley is mounted to the corresponding bevelled surface of the supporting body by a spindle. The spindle comprises a spindle body and a spindle head. The spindle body passes through a central aperture of the redirecting pulley. The central aperture is a through-hole which extends perpendicularly between the mounting surface and the opposing surface of the redirecting pulley. The spindle body passes through the central aperture of the redirecting pulley into a bore of the supporting body. Figures 12 and 13 illustrate the supporting body 509 in isolation. An exemplary implementation of the bore of the supporting body is depicted in these figures. The bore is a recess in the supporting body which tapers to a point. The spindle body passes through the initial opening of the bore and securely lodges in the tapered section. The spindle head is bigger than the central aperture of the redirecting pulley, and thus is unable to pass through the central aperture of the redirecting pulley. Consequently, the spindle head secures the redirecting pulley flush against the bevelled surface of the supporting body. The spindle head contacts at least a portion of the opposing surface of the redirecting pulley, through which contact the redirecting pulley is retained against the bevelled surface.

Referring to figure 14, the diameter of the bore 1401 through the supporting body is greater than the diameter of the spindle body 1403. The diameter of the central aperture 1402 of the redirecting pulley may be greater than the diameter of the spindle body 1403. Thus, the spindle body may loosely fit through the central aperture of the redirecting pulley. The spindle body loosely fits through the bore of the supporting body except for in the region in which it is secured to the bore, in the example above the tapered section. Typically, the bore through the supporting body is created by drilling through the bevelled surface of the supporting body during manufacture. Since the opening of the bore in the bevelled surface has a greater diameter than the spindle body, the precision of the angle at which the supporting body is drilled to create the bore is not critical. The spindle sits in the bore at the correct angle for the redirecting pulley to sit flush with the bevelled surface. It would have been critical that the angle of the bore was drilled very accurately if the fit of the spindle body through the bore was a tight fit and was the means by which the redirecting pulley was caused to rotate about the redirecting pulley axis 718,719. In that case the pulley would have been mounted tight on to the spindle which would have been mounted tight into the bore to stop

the pulley from precessing. Thus, there would have been no room for manufacturing deviations in the angle at which the hole was drilled through the supporting body. In the described implementation, however, the redirecting pulley is caused to rotate about the redirecting pulley axis 718,719 as a result of the redirecting pulley being held flush against a bevelled surface of the supporting body 509 which is perpendicular to the redirecting pulley axis 718,719. Thus, greater manufacturing variation in the accuracy of the angle at which the bore is drilled through the supporting body is acceptable in the described implementation.

The bevelled surfaces 1101 and 1102 of the supporting body are not parallel to each other. The bevelled surfaces may be symmetrical about a plane which is perpendicular to the first axis 510. The bevelled surfaces may be rotationally symmetrical about a plane which is perpendicular to the first axis 510. Specifically, the bevelled surfaces may be rotationally symmetrical about a line in a plane which is perpendicular to the first axis 510. When the instrument is in the straight configuration illustrated in figure 5a, the bevelled surfaces are rotationally symmetrical about the longitudinal axis of the shaft 511. This is second order rotational symmetry. The bevelled surfaces may be a reflection of each other in the plane which is perpendicular to the first axis 510.

Referring to figure 15, in one example, the supporting body 509 comprises grooves adjacent to each bevelled surface for seating a driving element. The supporting body comprises a groove 1501 adjacent the bevelled surface 1101 for seating the second one C2 of the third pair of driving elements. The driving element C2 is seated in the groove 1501 and partially enclosed by the first redirecting pulley 716. The supporting body comprises a groove 1502 adjacent the bevelled surface 1102 for seating the second one B2 of the second pair of driving elements. Groove 1502 is shown in figure 11. The driving element B2 is seated in the groove 1502 and partially enclosed by the second redirecting pulley 717.

The first, second and third pairs of driving elements extend through the instrument shaft from the distal end of the shaft connected to the articulation to the proximal end of the shaft connected to a drive mechanism of the instrument interface. Figures 17a and 17b illustrate two views of the first, second and third pairs of driving elements extending from the described articulation to an exemplary instrument interface 1701. In an exemplary implementation, the second and third pairs of driving elements overlap in the shaft so as to emerge from the proximal end of the shaft in a different arrangement to that at which they are in at the distal end of the shaft. Figure 16 illustrates cross-sections of the shaft depicting the positions of the driving elements.

Configuration (a) of figure 16 shows a cross-section of the shaft at the distal end of the shaft. In other words, configuration (a) shows the positions of the driving elements just as they have left the second set of pulleys 602. The driving elements Al and A2 are at opposing sides of the shaft after having left the first joint 506. The driving elements CI and B2 are adjacent each other on an opposing side of the shaft to the driving elements Bl and C2 which are also adjacent each other. The driving elements CI and B2 are offset from the driving elements Bl and C2 about an axis 1601 which is transverse to the axis 1602 connecting driving elements Al and A2. This is a result of the offset axes of the two pulleys of the second set of pulleys.

Configuration (b) of figure 16 shows a cross-section of the shaft at the proximal end of the shaft. In other words, configuration (b) shows the positions of the driving elements as they are about to exit the shaft into the instrument interface. The first pair of driving elements Al and A2 are on opposing sides of the shaft in a similar arrangement to their arrangement in configuration (a). The first pair of driving elements may be closer together, by virtue of them having moved slightly towards each other over the course of their extent through the shaft. In configuration (b), driving element Bl is located on an opposing side of the shaft to its location in configuration (a). In configuration (b), driving element CI is located on an opposing side of the shaft to its location in configuration (a). To achieve this, driving element Bl and driving element CI have not extended down the shaft parallel to the longitudinal axis of the shaft 511. Instead, driving element Bl and driving element CI have overlapped each other during their extent in the shaft. This overlapping occurs without the driving elements Bl and CI clashing because of their offset positions in configuration (a) owing to the pulleys of the second set of pulleys 602 having offset axes. Driving element B2 has moved a little in the shaft, but remained on the same side of the shaft as in configuration (a), so as to emerge at the proximal end of the shaft adjacent to driving element Bl. Driving element C2 has moved a little in the shaft, but remained on the same side of the shaft as in configuration (a), so as to emerge at the proximal end of the shaft adjacent to driving element CI.

The instrument interface comprises a further pulley arrangement around which the first, second and third pairs of driving elements are constrained to move. The driving elements Al, A2, Bl, B2, CI and C2 emerge at the proximal end of the shaft in a configuration which enables them to engage directly with components of the instrument interface. In one implementation, the driving elements emerge at the proximal end of the shaft as shown in configuration (b) in order to engage directly with the further pulley arrangement of the instrument interface described herein. Suitably, the first, second and third driving elements extend from the pulley arrangement at the distal end of the shaft to the instrument interface without wrapping around any intervening pulleys. Suitably, there are no intervening pulleys in the shaft around which the first, second and/or third pairs of driving elements are constrained to move.

As can be seen in figures 17a and 17b, the instrument interface is relatively flat. The instrument interface extends mostly in a central plane viewed head on in figure 17a. Suitably, the instrument shaft 504 is rigidly attached to the instrument interface 1701. The instrument shaft 504 does not rotate or otherwise move relative to the instrument interface 1701.

Suitably, the second axis 512 about which the end effector elements 502, 503 rotate is perpendicular to the central plane of the instrument interface. This is the case in the straight configuration of the instrument shown in figures 17a and 17b. Thus, in the straight configuration of the instrument, the jaws of the end effector are moveable in the central plane of the instrument interface.

A driving element may be a uniform component having the same shape and size along its length and constructed of the same material along its length. Alternatively, the driving element may be composed of different portions. In one example, the portion of the driving element which engages components of the instrument interface (such as pulleys and interface elements) is flexible. Similarly, the portion of the driving element which engages components of the distal end of the surgical instrument (such as the pulleys and joints in the articulation) is flexible. Between these two flexible portions are spokes 1702 illustrated in figures 17a and 17b. Thus, each pair of driving elements comprises two spokes and two flexible portions. Each pair of driving elements forms a loop. The loop comprises alternating spokes and flexible portions. The two spokes are predominantly or wholly enclosed in the instrument shaft. A distal flexible portion terminates at one end in the distal end of one of the spokes, and at the other end in the distal end of the other spoke. The distal flexible portion engages components of the articulation. A proximal flexible portion terminates at one end in the proximal end of one of the spokes, and at the other end in the proximal end of the other spoke. The proximal flexible portion engages components of the instrument interface. The spokes are stiffer than the flexible portions. Suitably, the spokes are rigid. The spokes may be hollow. Typically, the spokes have a larger diameter than the flexible portions. Thus, the flexible portions may be cables, and the spokes hollow tubes. The flexible portions may terminate where they meet the spokes. Alternatively, the spokes may encapsulate the material of the flexible portions. For example, the spokes may be rigid sheaths which cover flexible cables.

The spokes are stiffer than the flexible portions. Thus, by forming a pair of driving elements from spokes as well as flexible portions, the likelihood of the driving element stretching is reduced. For this reason, the proportion of each driving element which is a spoke is preferably maximised whilst ensuring that the spoke does not come into contact with components of the articulation or the instrument interface, and also that adjacent driving elements do not collide. The spokes are stronger than the flexible portions, and hence more resilient to compression and tension forces applied in any direction than the flexible portions. Thus, by incorporating the spokes, the driving element as a whole is stiffer and less likely to stretch. Thus, the lifetime of the driving element before it needs re-tensioning or replacing is extended.

In figure 18 the spokes of the driving elements Al, A2, Bl and CI are visible, labelled as Als, A2s, Bis and Cls respectively. Figure 18 depicts a straight configuration of the surgical instrument in which the end effector 501 is aligned with the shaft 504. As can be seen in figure 18, the distal flexible portion of driving element Al terminates in the spoke Als at a point 1801 along the longitudinal direction x of the shaft. The longitudinal direction x is the direction of the longitudinal axis 511 of the shaft. The distal flexible portion of driving element A2 terminates in the spoke A2s at a point 1802 along the longitudinal direction x of the shaft. The distal flexible portion of driving element Bl terminates in the spoke Bis at a point 1803 along the longitudinal direction x of the shaft. The distal flexible portion of driving element CI terminates in the spoke Cls at a point 1804 along the longitudinal direction x of the shaft. The distal flexible portions of driving elements B2 and C2 terminate in their respective spokes further towards the proximal end of the shaft, as can be seen in figure 17a.

As can be seen in figure 18, the longitudinal positions 1801, 1802, 1803 and 1804 at which the distal flexible portions of the driving elements terminate in the distal ends of the spokes are not coincident when the instrument is in the straight configuration depicted. Instead, the longitudinal positions 1801, 1802, 1803 and 1804 are offset from each other. In other words, the distal ends of the spokes of the driving elements are offset along the longitudinal direction of the shaft when the instrument is in the straight configuration. Specifically, the distal ends of adjacent spokes are offset along the longitudinal direction of the shaft in the straight configuration. The distal ends of spokes which are not adjacent to each other may be coincident along the longitudinal direction of the shaft in the straight configuration. For example, in figure 18, the non-adjacent spokes Als and A2s both terminate at the same point 1801,1802 along the longitudinal direction of the shaft. Suitably, the distal ends of the spokes of the driving elements are offset along the longitudinal direction of the shaft in every configuration of the surgical instrument. Specifically, suitably, the distal ends of adjacent spokes are offset along the longitudinal direction of the shaft in every configuration of the surgical instrument.

As previously discussed in relation to figure 16, the driving elements do not all extend parallel to each other in the shaft in an implementation in which driving elements pass directly from the pulley arrangement at the distal end of the shaft to the pulley arrangement in the instrument interface without moving around any intervening pulleys. The first one of the first pair of driving elements Al extends substantially parallel to the second one of the first pair of driving elements A2 in the shaft. Driving elements Al and A2 may move slightly closer to each other over the course of the length of the shaft in the direction from the articulation to the instrument interface. The first one of the second pair of driving elements Bl extends at an angle to the second one of the second pair of driving elements B2 in the shaft. Driving element Bl also extends at an angle to driving elements Al, A2, CI and C2 down the shaft. Driving element B2 extends at an angle to driving elements Al, A2, CI and C2 down the shaft.

The first one of the third pair of driving elements CI extends at an angle to the second one of the third pair of driving elements C2 in the shaft. Driving element CI also extends at an angle to driving elements Al, A2, Bl and B2 down the shaft. Driving element C2 extends at an angle to driving elements Al, A2, Bl and B2 down the shaft.

The longitudinal positions of the distal ends of the spokes are selected such that the spokes do not collide when the instrument is being articulated. Since the spokes have a larger diameterthan the flexible portions, although the flexible portions can extend down the length of the shaft without colliding the spokes may not be able to. Suitably, the longitudinal positions of the distal ends of the spokes in the straight configuration of the instrument are such that for any configuration of the end effector, no portion of any driving element contacts a portion of another driving element. Suitably, the positions of the proximal and distal ends of the spokes in the straight configuration are selected so as to maximise the spoke length whilst satisfying the condition that the driving elements will not contact. The spokes are stiffer than the flexible portions. Thus, this maximises the stiffness of the driving elements whilst enabling them to wrap around components in the articulation and instrument interface. This maximises the strength of the driving elements whilst enabling them to wrap around components in the articulation and instrument interface.

In figure 19a the spokes of the driving elements Al, A2, Bl and CI are visible, labelled as Als, A2s, Bis and Cls respectively. Figure 19a depicts a non-straight configuration of the surgical instrument in which the end effector 501 is not aligned with the shaft 504. As can be seen in figure 19a, the proximal flexible portion of driving element Al terminates in the spoke Als at a point 1901 along the longitudinal direction x of the shaft. The longitudinal direction x is the direction of the longitudinal axis 511 of the shaft. The proximal flexible portion of driving element A2 terminates in the spoke A2s at a point 1904 along the longitudinal direction x of the shaft. The proximal flexible portion of driving element Bl terminates in the spoke Bis at a point 1902 along the longitudinal direction x of the shaft. The proximal flexible portion of driving element CI terminates in the spoke Cls at a point 1903 along the longitudinal direction x of the shaft. The proximal flexible portions of driving elements B2 and C2 terminate in their respective spokes further towards the distal end of the shaft, as can be seen in figure 17a. The spokes may terminate in the proximal flexible portions inside the shaft, as is the case in the example shown for driving elements B2 and C2. The spokes may terminate in the proximal flexible portions inside the instrument interface, as is the case in the example shown for driving elements Al, A2, Bl and CI. Some spokes may terminate in the proximal flexible portions inside the shaft and some spokes may terminate in the proximal flexible portions inside the instrument interface. In the design of the instrument interface depicted in figure 19a, the driving elements B2 and C2 engage pulleys as they enter the instrument interface from the shaft, thus the spokes of driving elements B2 and C2 terminated in their proximal flexible portions in the shaft (not shown) to enable the proximal flexible portions to engage the pulleys. Driving elements Al, A2, Bl and CI all extend some distance into the instrument interface before engaging with components of the instrument interface, thus the spokes of driving elements Al, A2, Bl and CI are able to extend into the instrument interface.

WE CLAIM

A robotic surgical instrument comprising:

a shaft;

an end effector element;

an articulation connecting the end effector element to the shaft, the articulation comprising:

a first joint driveable by a first pair of driving elements, the first joint permitting the end effector element to rotate about a first axis transverse to a longitudinal axis of the shaft, the rotation of the end effector element about the first axis bounded by an extreme rotation angle relative to the longitudinal axis, and

a second joint driveable by a second pair of driving elements; and a pulley arrangement around which the second pair of driving elements is constrained to move, the pulley arrangement comprising:

a first set of pulleys rotatable about the first axis, and

a second set of pulleys located relative to the first set of pulleys such that at the extreme rotation angle the second pair of driving elements is retained in contact with both the first and second sets of pulleys.

A robotic surgical instrument as claimed in claim 1, wherein the second set of pulleys is located such that the second pair of driving elements is retained in contact with both the first and second sets of pulleys at any rotation angle of the end effector element relative to the longitudinal axis.

A robotic surgical instrument as claimed in claim 1 or 2, wherein the second joint permits the end effector element to rotate about a second axis transverse to the first axis.

4. A robotic surgical instrument as claimed in any preceding claim, wherein each pulley of the second set of pulleys is rotatable about an axis parallel to the first axis.

5. A robotic surgical instrument as claimed in claim 4, wherein each pulley of the second set of pulleys is rotatable about an axis offset from the first axis.

6. A robotic surgical instrument as claimed in claim 4 or 5, wherein the second set of pulleys comprises a first pulley rotatable about a third axis, and a second pulley rotatable about a fourth axis, the third axis being offset from the fourth axis.

7. A robotic surgical instrument as claimed in any preceding claim, wherein a distal end of the shaft is connected to the articulation, and a proximal end of the shaft is connected to a drive mechanism for driving the first and second pairs of driving elements, wherein the second set of pulleys is located between the first set of pulleys and the proximal end of the shaft.

8. A robotic surgical instrument as claimed in claim 7, wherein the second set of pulleys is located inside the shaft.

9. A robotic surgical instrument as claimed in claim 7, wherein the articulation comprises the second set of pulleys.

10. A robotic surgical instrument as claimed in any preceding claim, wherein:

the first set of pulleys comprises a first pulley and a second pulley located on opposing sides of the first joint; and

the second set of pulleys comprises a first pulley and a second pulley located on opposing sides of the first joint.

11. A robotic surgical instrument as claimed in claim 10, wherein the second pair of driving elements is constrained to move around opposing sides of the first and second pulley of the first set of pulleys.

12. A robotic surgical instrument as claimed in claim 10 or 11, wherein the second pair of driving elements is constrained to move around opposing sides of the first and second pulleys of the second set of pulleys.

13. A robotic surgical instrument as claimed in any preceding claim, further comprising a further end effector element, wherein the articulation further comprises a third joint driveable by a third pair of driving elements, the third pair of driving elements constrained to move around the pulley arrangement, the second set of pulleys being located relative to the first set of pulleys such that at the extreme rotation angle the third pair of driving elements is retained in contact with both the first and second sets of pulleys.

14. A robotic surgical instrument as claimed in claim 10, wherein the third joint permits the further end effector element to rotate about the second axis.

15. A robotic surgical instrument as claimed in claim 13 or 14 when dependent on claim 10, 11 or 12, wherein each pulley of the first and second sets of pulleys comprises a pair of pulley elements, the pair of pulley elements comprising an inside pulley element and an outside pulley element, the inside pulley element located between the outside pulley element and the first joint, each pulley element comprising a groove for seating a driving element.

16. A robotic surgical instrument as claimed in claim 15, wherein:

the second pair of driving elements is constrained to move about the inside pulley element of the first pulley of the second set of pulleys and the outside pulley element of the second pulley of the second set of pulleys; and

the third pair of driving elements is constrained to move about the outside pulley element of the first pulley of the second set of pulleys and the inside pulley element of the second pulley of the second set of pulleys.

17. A robotic surgical instrument as claimed in claim 15 or 16, wherein:

the second pair of driving elements is constrained to move about the inside pulley element of the first pulley of the first set of pulleys and the outside pulley element of the second pulley of the first set of pulleys; and

the third pair of driving elements is constrained to move about the outside pulley element of the first pulley of the first set of pulleys and the inside pulley element of the second pulley of the first set of pulleys.

18. A robotic surgical instrument as claimed in any of claims 15 to 17, wherein for each pulley, one pulley element of the pair of pulley elements abuts the other pulley element of the pair of pulley elements.

19. A robotic surgical instrument as claimed in any of claims 13 to 18, wherein the second pair of driving elements and the third pair of driving elements have the same length for all rotation angles of the end effector element relative to the longitudinal axis.

20. A robotic surgical instrument as claimed in any of claims 13 to 19, wherein the first and second end effector elements are opposing first and second jaws of an end effector.

21. A robotic surgical instrument as claimed in any preceding claim, wherein the pairs of driving elements comprise flexible portions and spokes.

22. A robotic surgical instrument as claimed in any preceding claim, wherein the pairs of driving elements are cables.

23. A robotic surgical instrument as claimed in any preceding claim, wherein the pairs of driving elements resist compression and tension forces.