GB2621588A

GB2621588A - Surgical instrument disengagement

Info

Publication number: GB2621588A
Application number: GB2211914.3A
Authority: GB
Inventors: Stuart Gregory; James Wildin Tucker Edward; Moore David; Rigas Paul; Ascah-Coallier Isabelle; Moss Ethan
Original assignee: CMR Surgical Ltd
Current assignee: CMR Surgical Ltd
Priority date: 2022-08-15
Filing date: 2022-08-15
Publication date: 2024-02-21
Also published as: WO2024038265A1; GB202211914D0

Abstract

A control unit 309 for a surgical robotic system comprising a robotic arm 300 with a drive assembly having a first interface element to actuate a first joint of an instrument 306 when engaged with the robotic arm. The instrument has an end effector with first and second end effector elements, the first being moveable with respect to the second about the first joint. The control unit receives a signal from a user input device, that may be located on the robot arm 313, indicating intended disengagement of the instrument from the robotic arm, and in response cause the system to change from a first state in which the first effector element exerts a gripping force on the second end effector element, to a second state in which it does not. The effector elements may be in contact in the second state. The second end effector may also be driven.

Description

SURGICAL INSTRUMENT DISENGAGEMENT

FIELD OF THE INVENTION

This invention relates to a mechanism to allow removal of a surgical instrument from the end of a robotic arm, for example following the occurrence of a fault in a surgical robotic system

BACKGROUND

It is known to use robots for assisting and performing surgery. Figure 1 illustrates a typical surgical robot 100 which comprises 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 and joints of the end effector. This can allow the end effector to be positioned accordingly to perform a surgical procedure where it may be required to, for example, grip a piece of tissue or a piece of surgical thread to thread a needle for use in a suturing procedure.

The instrument may conveniently be removable from a robot arm to allow the instrument to be cleaned. The distal end of a robot arm may comprise a drive assembly for driving parts of the instrument to move.

Increases to the amount of grip that can provided by a surgical instrument may have the consequence of making the instrument difficult to remove from the robotic arm. For example, when a fault occurs in the surgical robotic system when jaws of an instrument are in a configuration where they are gripping tightly, it may be difficult to remove the instrument due to friction between engagement features on the instrument and actuators in the drive assembly at the distal end of the robot arm, as the friction between the engagement features and actuators increases as the driving force between them increases.

As a result, if a fault occurs in a part of the surgical system while an end effector of an instrument is in a gripping configuration, it may be difficult for the surgeon or the bedside team to reduce the forces to allow the instrument to be disengaged from the robot arm.

SUMMARY

According to a first aspect, there is provided a control unit for a surgical robotic system, the surgical robotic system comprising a robotic arm comprising a drive assembly having a first drive assembly interface element configured to provide mechanical drive for actuating a first joint of an instrument when the robotic arm engages with the instrument, the instrument having an end effector comprising a first end effector element and a second end effector element, the first end effector element being moveable with respect to the second end effector element about the first joint, the control unit being configured to control the drive assembly and comprising one or more processors configured to: receive a signal from an input device when a user inputs a request to disengage the instrument from the robotic arm; and in response to receiving the signal, cause the first drive assembly interface element to move from a first position in which the first end effector element exerts a gripping force on the second end effector element to a second position in which the first end effector element does not exert a gripping force on the second end effector element In response to receiving the signal, the one or more processors may be configured to cause the drive assembly to drive the first drive assembly interface element to actuate the first joint such that the first end effector element does not exert a gripping force on the second end effector element. In response to receiving the signal, the one or more processors may be configured to cause the first drive assembly interface element to move from a first position in which the first end effector element is driven to exert a gripping force on the second end effector element to a second position in which the first end effector element is driven to not exert a gripping force on the second end effector element. In response to receiving the signal, the one or more processors may be configured to cause the first drive assembly interface element to move from a first position which causes the first end effector element to exert a gripping force on the second end effector element to a second position which causes the first end effector element to not exert a gripping force on the second end effector element.

In the second position, the first end effector element may be in contact with the second end effector element. In the first position, the first end effector element may be in contact with the second end effector element.

The first drive assembly interface element may be configured to drive a first instrument interface element of the instrument when the robotic arm engages the instrument. The first drive assembly interface element may be configured to engage the first instrument interface element.

The first instrument interface element may be connected to a first pair of driving elements for driving the first joint.

In response to receiving the signal, the one or more processors may be configured to cause the first drive assembly interface element to move from the first position to the second position to drive the first instrument interface element to move from a corresponding first position to a corresponding second position.

The drive assembly may comprise a guide constraining the displacement of the first drive assembly interface element within the drive assembly.

The drive assembly may comprise a position sensor configured to provide a position signal to the control unit indicating the position of the first drive assembly interface element within the drive assembly.

The first position may be a first longitudinal position within the drive assembly. The second position may be a second longitudinal position within the drive assembly.

The robotic arm may extend between a base and a terminal limb. The terminal limb may have a longitudinal axis. The terminal limb may be connected to an adjacent limb in the robotic arm by a joint which permits the terminal limb to rotate about the longitudinal axis of the terminal limb. The terminal limb may comprise the drive assembly.

The first drive assembly interface element may be engageable with the first instrument interface element on the longitudinal axis of the terminal limb. The first drive assembly interface element may be linearly displaceable in a direction parallel to the longitudinal axis of the terminal limb so as to drive the first instrument interface element in a direction parallel to the longitudinal axis of the terminal limb. The second position may be a position in which the first drive assembly interface element does not exert a force on the first instrument interface element in a direction parallel to the longitudinal axis of the terminal limb.

At the time of the request to disengage the instrument from the robotic arm, the drive assembly may be configured to drive the first joint such that the first end effector element exerts a gripping force on the second end effector element.

The end effector may further comprise a second joint about which the second end effector element is moveable with respect to the first end effector element.

The drive assembly may comprise a second drive assembly interface element configured to provide mechanical drive for actuating the second joint of the instrument when the robotic arm engages with the instrument.

The one or more processors may be further configured to, in response to receiving the signal, cause the second drive assembly interface element to move from a position in which the second end effector element exerts a gripping force on the first end effector element to a position in which the second end effector element does not exert a gripping force on the first end effector element.

In response to receiving the signal, the one or more processors may be configured to cause the drive assembly to drive the second drive assembly interface element to actuate the second joint such that the second end effector element does not exert a gripping force on the first end effector element.

The second drive assembly interface element may be configured to drive a second instrument interface element of the instrument when the robotic arm engages the instrument. The second instrument interface element may be connected to a second pair of driving elements for driving the second joint.

The instrument may further comprise an articulation having a third joint about which the end effector can be driven to adopt a range of positions relative to a longitudinal axis of a shaft of the instrument.

The drive assembly may further comprise a third drive assembly interface element configured to drive a third instrument interface element of the instrument when the robotic arm engages the instrument. The third instrument interface element may be connected to a third pair of driving elements for driving the third joint.

The one or more processors may be further configured to, in response to receiving the signal, not cause the drive assembly to drive the third joint. The one or more processors may be further configured to, in response to receiving the signal, not cause the drive assembly to move the third drive assembly interface element.

The robotic arm may comprise the input device.

The one or more processors may be configured to receive the signal in response to the user engaging the input device for at least a predetermined time period. The predetermined time period may be at least 1 second. The predetermined time period may be at least 1.5 seconds. The predetermined time period may be less than, for example, 3 seconds. The input device may return to an initial state (from an engaged state) when the user ends their engagement with the input device.

The one or more processors may be configured to output one or more of an audible signal, a visual signal and a haptic signal when the user has engaged with the input device for at least the predetermined time period.

The end effector may comprise a pair of jaws. The first end effector element may be a first jaw of a pair of jaws. The second end effector element may be a second jaw of a pair of jaws.

The surgical robotic system may comprise one or more additional input devices configured to control the robotic arm and/or the instrument to perform a surgical procedure. The input device may be a separate input device to the one or more additional input devices. The one or more additional input devices may be at a location remote from the robotic arm. The one or more additional input devices may be located at a command interface remote from the robotic arm. It may not be possible to control motion of the robotic arm and/or the end effector using the one or more additional input devices when the processor receives an indication of a fault in the surgical robotic system.

The one or more processors may be further configured to cause the first drive assembly interface element to move from the first position to the second position in response to the one or more processors receiving an indication of a fault. The fault may be a fault in the surgical robotic system. The fault may be a fault relating to a component of the surgical robotic system other than the robotic arm and/or the instrument.

The fault may be a fault relating to one or more of a command interface remote from the robotic arm configured to allow a surgeon to control the robotic arm, a further robotic arm of the surgical robotic system and an imaging device of the surgical robotic system. The fault may prevent the robotic arm and/or the instrument from being controlled using the one or more additional input devices. The fault may prevent the robotic arm and/or the instrument from being controlled via the command interface.

According to a second aspect there is provided a surgical robot comprising: a robotic arm comprising a drive assembly having a first drive assembly interface element configured to provide mechanical drive for actuating a first joint of an instrument when the robotic arm engages with the instrument, the instrument having an end effector comprising a first end effector element and a second end effector element, the first end effector element being moveable with respect to the second end effector element about the first joint; and the control unit having any of the features described above.

According to a further aspect there is provided a surgical robotic system comprising: an instrument having an end effector, the end effector comprising a first end effector element and a second end effector element and having a first joint about which the first end effector element is moveable with respect to the second end effector element; a robotic arm comprising a drive assembly having a first drive assembly interface configured to provide mechanical drive for actuating the first joint when the robotic arm engages the instrument; an input device whereby a user can input a request to disengage the instrument from the robotic arm; and a control unit having any of the features described above.

According to a further aspect there is provided a method of controlling a robotic arm in a surgical robotic system, the surgical robotic system comprising a robotic arm comprising a drive assembly having a first drive assembly interface element configured to provide mechanical drive for actuating a first joint of an instrument when the robotic arm engages with the instrument, the instrument having an end effector comprising a first end effector element and a second end effector element, the first end effector element being moveable with respect to the second end effector element about the first joint, the method comprising: receiving a signal from an input device when a user inputs a request to disengage the instrument from the robotic arm; and in response to receiving the signal, cause the drive assembly to drive the first drive assembly interface element to move from a first position in which the first end effector element exerts a gripping force on the second end effector element to a second position in which the first end effector element does not exert a gripping force on the second end effector element.

According to another aspect, there is provided a computer-readable storage medium have stored thereon computer readable instructions that when executed at a computer system comprising one or more processors cause the one or more processors to perform the method above. The computer-readable storage medium may be a non-transitory computer-readable storage medium.

BRIEF DESCRIPTION OF THE FIGURES

The present disclosure will now be described by way of example with reference to the accompanying drawings.

In the drawings: Figure 1 illustrates a surgical robot performing a surgical procedure; Figure 2 illustrates a surgical instrument; Figure 3 illustrates a surgical robot; Figures 4a and 4b illustrate a distal end of a surgical instrument; Figures 5a and 5b illustrate a pulley arrangement of the distal end of the surgical instrument of figures 4a and 4b in a straight configuration; Figure 6 illustrates an instrument interface; Figure 7 illustrates a drive assembly interface of a robot arm with attached interface structure; Figure 8 illustrates an instrument being positioned into engagement with a robot arm;

DETAILED DESCRIPTION

Figure 3 illustrates a surgical robot having an arm 300 which extends from a base 301. The arm comprises a number of rigid limbs 302. The limbs are coupled by revolute joints 303. The most proximal limb 302a is coupled to the base by joint 303a. It and the other limbs are coupled in series by further ones of the joints 303. Suitably, a wrist 304 is made up of four individual revolute joints. The wrist 304 couples one limb (302b) to the most distal limb (302c) of the arm. The most distal limb 302c carries an attachment 305 for a surgical instrument 306. Each joint 303 of the arm has one or more motors 307 which can be operated to cause rotational motion at the respective joint, and one or more position and/or torque sensors 308 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 3.

The arm terminates in an attachment 305 for interfacing with the instrument 306. Suitably, the instrument 306 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 305 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 306 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 threader for suturing, a stapler, or an electrosurgical tool. 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 309. A control unit 309 comprises a processor 310 and a memory 311. Memory 311 stores in a non-transient way software that is executable by the processor to control the operation of the motors 307 to cause the arm 300 to operate in the manner described herein. In particular, the software can control the processor 310 to cause the motors (for example via distributed controllers) to drive in dependence on inputs from the sensors 308 and from a surgeon command interface 312. The control unit 309 is coupled to the motors 307 for driving them in accordance with outputs generated by execution of the software. The control unit 309 is coupled to the sensors 308 for receiving sensed input from the sensors, and to the command interface 312 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 312 comprises one or more input devices whereby a user can ordinarily request motion of the arm and/or the end effector in a desired way during a surgical procedure. 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 311 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 312 can control the instrument 306 to move in such a way as to perform a desired surgical procedure. The control unit 309 and/or the command interface 312 may be remote from the arm 300.

A further input device 313 may be located on the robot arm. Alternatively, the input device 313 may be located elsewhere in the surgical system, such as on the command interface 312 or at a location remote from the robot arm. The input device 313 could, for example, be a manually operable mechanical input device such as a button, or a contactless input device comprising an optical gesture sensor. The input device 313 may allow a user to make requests to control the motion of the end effector outside of normal operation during a surgical procedure. For example, the user may request to move the end effector to allow disengagement of the instrument from the robot arm following a fault in the surgical robotic system, as will be described in more detail later. The input device 313 is coupled to the control unit 309, for example using electrical or optical cables or a wireless connection.

Figures 4a and 4b illustrate opposing views of the distal end of a surgical instrument. In Figures 4a and 4b, the end effector 501 comprises a pair of end effector elements 502, 503, which in Figures 4a and 4b 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. In other configurations of the distal end of the instrument, articulation about all of the first, second and third joints can be driven relative to the straight configuration of Figures 5a and 5b.

Returning to Figures 4a and 4b, 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 4a and 4b, the first joint 506 is driven by a first pair of driving elements Al,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 Cl,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 4a and 4b. 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 4a and 4b 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 5a and 5b. The supporting body 509 is not shown in Figures 5a and 5b 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.

It will be appreciated that the articulations shown here are examples and that the surgical instrument may comprise any number of joints. The one or more joints may comprise pitch joints, yaw joints, roll joints (rotation about an axis generally along the extent of the instrument), or a combination thereof. The instrument may further comprise additional pulleys and cables for actuating further instrument joints. The instrument may also additionally comprise gear reductions etc. The robotic arm comprises a drive assembly for selectively actuating the joints of the instrument (e.g. to pivot the wrist member and/or the grippers of the end effector). The drive assembly may be configured to mechanically drive these joints. The drive assembly may be housed within the robotic arm. This is desirable because it reduces the cost and size of the instrument, which may be particularly important if the instruments are disposable. The drive assembly may be powered by one or more motors or servomechanisms that produce linear and/or rotary motion. The drive assembly may be capable of actuating each of the instrument joints separately and independently of each other. That is, the drive assembly can selectively actuate the joints. The drive assembly may be capable of actuating a plurality of joints simultaneously.

The drive assembly operates to actuate selected joints of the instrument by causing the appropriate driving elements within the instrument to undergo reciprocal motion. The drive assembly may be configured to actuate a selected joint or a selected plurality of joints by driving the appropriate pulleys within the instrument.

As will be described in more detail below, each pair of driving elements of the instrument engages a single instrument interface element in the instrument interface. Each driving element engages an instrument interface element in the instrument interface. A single instrument interface element drives a pair of driving elements. Each driving element is driven independently by a single instrument interface. In alternative arrangements, there may be a compound driving motion in which more than one instrument interface element drives a single driving element, a single instrument interface element drives more than one pair of driving elements, or a plurality of instrument interface elements collectively drive a plurality of driving elements.

Figures 6 and 7 illustrate an exemplary mechanical interconnection of the drive assembly interface and the instrument interface in order to transfer drive from the robot arm to the instrument. The shaft 504 of the instrument terminates in the instrument interface 800. The instrument interface 800 comprises a plurality of instrument interface elements 803, 804, 805. Pairs of driving elements (Al, A2), (B1, B2), (Cl, C2) extend into the instrument interface 800 from the end of the shaft 504. Each pair of driving elements terminates in one of the instrument interface elements. In the example shown in Figure 6: driving element pair Al, A2 terminates in instrument interface element 805; driving element pair Bl, B2 terminates in instrument interface element 803; and driving element pair Cl, C2 terminates in instrument interface element 804.

Figure 6 illustrates three instrument interface elements and three driving element pairs. In other examples, there may be greater than or fewer than three instrument interface elements. There may be greater than or fewer than three driving element pairs. In Figure 6 there is a one-to-one relationship between instrument interface elements and driving element pairs. In other examples, there may be any other coupling relationship between the instrument interface elements and driving element pairs. For example, a single instrument interface element may drive more than one pair of driving elements. In another example, more than one instrument interface element may drive a single pair of driving elements.

The instrument interface elements are displaceable within the instrument interface. In the example shown, the instrument interface elements are slideable along rails. Instrument interface element 803 is slideable along rail 806 and instrument interface element 805 is slideable along rail 807. Instrument interface element 804 is slideable along a rail (not shown). Each instrument interface element is displaceable along a direction parallel to the direction of elongation of the pair of driving elements which that instrument interface element holds captive. Each instrument interface element is displaceable in a direction parallel to the longitudinal axis 808 of the instrument shaft 504. When the instrument interface element moves along its rail, it causes a corresponding movement to the driving element pair secured to it. Thus, moving an instrument interface element drives motion of a driving element pair and hence motion of a joint of the instrument.

In the example of Figure 6, each instrument interface element comprises a fin 809, 810, 811 which is the portion of the instrument interface element which engages the drive assembly interface element. In another example, each drive assembly interface element comprises a fin, and each instrument interface element comprises a socket for receiving the fin of the corresponding drive assembly interface element. Each instrument interface element is therefore engageable with a drive assembly interface element.

Figure 7 illustrates an exemplary drive assembly interface 900 at the end of a robot arm 901. Drive assembly interface 900 mates with instrument interface 800. Drive assembly interface 900 comprises structure for receiving the instrument interface elements of the instrument interface of Figure 6. Specifically, drive assembly interface elements 902, 903, 904 receive instrument interface elements 803, 804, 805. In the example shown, each drive assembly interface element comprises a socket for receiving the fin of the corresponding instrument interface element. Socket 905 of drive assembly interface element 902 receives fin 809 of instrument interface element 803. Socket 906 of drive assembly interface element 904 receives fin 810 of instrument interface element 805. Socket 907 of drive assembly interface element 903 receives fin 811 of instrument interface element 804.

Figure 7 illustrates three drive assembly interface elements. In other examples, there may be greater than or fewer than three drive assembly interface elements. In Figures 6 and 7 there is a one-to-one relationship between instrument interface elements and drive assembly interface elements. In other examples, there may be any other coupling relationship between the instrument interface elements and drive assembly interface elements. For example, a single drive assembly interface element may drive more than one instrument interface elements. In another example, more than one drive assembly interface elements may drive a single instrument interface element.

Each drive assembly interface element is displaceable within the drive assembly. This displacement is driven. For example, the displacement may be driven by a motor and lead screw arrangement. In the example shown, the drive assembly interface elements are slideable along rails. Each drive assembly interface element is displaceable along a direction parallel to the longitudinal axis 908 of the terminal limb 909 of the robot arm. When the drive assembly interface element moves along its rail, it causes a corresponding movement to the instrument interface element that it holds captive. Thus, driving motion of a drive assembly interface element drives motion of an instrument interface element which drives articulation of the end effector of the instrument.

Figure 8 illustrates the instrument being placed into engagement with the robot arm. When instrument interface element 803 and drive assembly interface element 902 are engaged, instrument interface element 804 and drive assembly interface element 903 are engaged, and instrument interface element 805 and drive assembly interface element 904 are engaged, the instrument interface elements and the drive assembly interface elements are all displaceable in the same direction. This direction is parallel to both the longitudinal axis of the terminal limb of the robot arm 908 and the longitudinal axis of the instrument shaft 808.

In other words, the drive assembly interface elements are engageable with their corresponding instrument interface element on the longitudinal axis of the terminal limb 908. The drive assembly interface elements are linearly displaceable in a direction parallel to the longitudinal axis of the terminal limb 908 so as to drive their corresponding instrument interface elements in a direction parallel to the longitudinal axis of the terminal limb.

The distal end of the robot arm comprises a first surface 704 which faces the surgical instrument when the instrument is attached to the robot arm (see Figure 8). Specifically, the first surface 704 faces the instrument interface 800.

In some circumstances, there may be a fault with the instrument, the robot arm or another component of the robotic surgical system when the instrument is being driven to be in a gripping state wherein one or more of the end effector elements 502, 503 exerts a gripping force on the other of the end effector elements. In this case, it may be difficult to remove the instrument from the robot arm. The difficulty of removal may be due to friction between the instrument interface elements and the drive assembly interface elements, which increases as the force between them increases as the drive assembly interface elements drive the instrument interface elements to move.

It may be desirable to remove the instrument from the robot arm to clear the operative area in short space of time after the fault has occurred, for example within 30 seconds.

As mentioned above, the surgical robotic system may comprise an input device 313 which a user, such as a surgeon or a member of the operating theatre team, can engage with to input a request to disengage the instrument from the robot arm. The input device may be located on the robot arm. Alternatively, the input device may be located at a different part of the surgical robotic system, such as the command interface 312 or another location remote from the robot arm, or on a robot arm different to the robot arm carrying the instrument (for example, on another robot arm carrying an imaging device such as an endoscope).

In one example, the input device 313 is a button that is engageable by a user, for example by the user depressing the button, to request disengagement of the instrument from the arm. Engagement of the input device by the user can cause the disengagement request to be transmitted to the control unit of the robot arm. The control unit therefore receives a signal from the input device when the user inputs a request via the input device to disengage the instrument from the robot arm.

In the example shown in Figure 3, the robot arm extends between a base and a terminal limb 302c. The terminal limb 302c is connected to an adjacent limb 302b in the robotic arm by a joint which permits the terminal limb to rotate about a longitudinal axis of the terminal limb. The terminal limb comprises the drive assembly. In this example, the input device 313 is located on the adjacent limb 302b, proximal to the elbow joint of the robot arm (the joint between adjacent limb 302b and the next limb of the robot arm.

The user can use the input device 313 to make a request to the control unit to allow disengagement of the instrument from the robot arm. For example, where input device 113 is a button, the user may make the request by pressing the button. In some implementations, to make the request to disengage the instrument from the robot arm, the user can engage continuously with the input device 313 for at least a predetermined time period. The predetermined time period may be, for example, 1 second, or 1.5 seconds. The benefit of using a predetermined time period longer than the time typically taken for a user to depress a button and then immediately release it (which may be, for example, one tenth of a second) is that the input device and/or the control unit can differentiate this request from other requests that the user may make via input device 313, as will be described in more detail below. The input device 313 may only be temporarily depressed when the user engages with it. The user can release the input device after engaging with it.

In response to the user making a request to disengage the instrument from the robot arm, for example by engaging with the input device 313 for at least a predetermined time period as described above, the control unit 309 is configured to receive a signal from the input device 313.

To alert the user that they have successfully requested disengagement of the instrument from the robot arm, the control unit may be configured to output an audible signal and/or a visual signal and/or a haptic or vibrational signal when the user has engaged with the input device for at least the predetermined time period. An audible flag such as an alarm, or a visual flag such as a flashing light or icon, may be output. The audible or visual flag following the depression of the input device for more than the predetermined time period may be delayed until the instrument relaxation process (i.e. the movement of the drive assembly interface element(s) to move the end effector to a closed configuration, as described below) has completed. This audible or visual flag can act as a prompt for the user to release the input device.

The input device 313 may also be used to perform other functions. For example, a user engaging with the input device for a shorter time than the predetermined time period (for example, by pressing a button and immediately releasing it) may be used to request a change in an operation mode of the robot arm.

However, the input device 313 is preferably not used to control movement of the robot arm or the instrument during normal operation (i.e. to control movement of the arm to perform a standard surgical procedure). Therefore, the input device 313 may be used to perform functions different to other input devices on the command interface 312.

The user engaging with the input device 313 for more than the predetermined time period may also be used to perform other functions when the instrument is not engaged with the robot arm. For example, this may be used to transition the robot from a mode in which a virtual pivot point (VPP) for the instrument is set to an unlocked mode where the VPP is not set. The VPP is a fixed point that the instrument pivots around. The instrument can be positioned accordingly so that the VPP is located inside a port in the patient's skin.

In response to receiving the signal from the input device when the user inputs a request to disengage the instrument from the robot arm, the control unit can cause the drive assembly to drive one or more joints of the instrument to cause the end effector 501 to transition from a state in which it is gripping to a state in which it is not gripping. The control unit may cause the drive assembly to drive one or more joints of the instrument to cause the end effector 501 to transition from a state in which it is gripping to a state in which it is closed, for example where the first and second end effector elements 502, 503 are in contact but each end effector element is not exerting a gripping force on the other.

At the time of the control unit receiving the signal, one or more of the end effector elements 502, 503 may be being driven by their corresponding drive assembly interface elements 902, 903 and instrument interface elements 803, 804 to exert a gripping force on the other of the end effector elements 502, 503. This state may be referred to as the end effector being in an 'overclosed' state. In the overclosed state, one or more of the end effector elements 502, 503 is configured to exert a gripping force on the other of the end effector elements. A state in which the end effector elements 502, 503 are in contact with one another but each end effector element is not configured to exert a gripping force on the other may be referred to as the end effector being in a 'closed' state. When the end effector elements 502, 503 are in contact with one another but each end effector element is not configured to exert a gripping force on the other, the frictional forces between the drive assembly interface element(s) and the corresponding instrument interface element(s) that control the spread of the end effector are minimal. This can allow for easier disengagement of the instrument from the drive assembly.

Although the end effector elements of a perfectly rigid instrument may not move as a result of the above-described instrument relaxation, in practice some movement of the end effector element(s), of the order of a few millimetres, may be observed due to tensions in the instrument being relaxed.

In the examples of the instrument, drive assembly and instrument interface illustrated in Figures 4a to 8, there are three instrument interface elements and three drive assembly interface elements. In these examples, two of the three drive assembly interface elements and their corresponding instrument interface elements drive the spread (i.e. opening and closing) of the end effector 501 (which in this example is a pair of jaws). In the examples shown in Figures 4a, 4b, 5a and 5b, articulation 505 comprises joints which permit the end effector 501 to move relative to the shaft 504. Joint 506 permits the end effector 501 to rotate about axis 510 transverse to the longitudinal axis of the shaft 511. Joint 507 permits the first end effector element 502 to rotate about axis 512. Joint 513 permits the second end effector element 503 to rotate about axis 512.

As mentioned above, the drive assembly comprises multiple drive assembly interface elements which drive the joints of the instrument. In Figures 6 to 8, drive assembly interface elements 902, 903, 904 receive instrument interface elements 803, 804, 805 respectively. Driving element pair Al, A2 drive the first joint 506 and terminate in instrument interface element 805, which engages with drive assembly interface element 904. Driving element pair Bl, B2 drive the second joint 507 and terminate in instrument interface element 803, which engages with drive assembly interface element 902. Driving element pair Bl, B2 are connected at their opposite end (opposite to the end connected to the instrument interface element 803) to the first end effector element 502. Driving element pair Cl, C2 drive the third joint 513 and terminate in instrument interface element 804, which engages with drive assembly interface element 903. Driving element pair Cl, C2 are connected at their opposite end (opposite to the end connected to the instrument interface element 804) to the instrument interface element 804 to the second end effector element 503.

In this example, both end effector elements 502, 503 are moveable relative to each other about their respective joints 507, 513. Therefore, on receiving the signal from the input device, the control unit can move one or more of drive assembly interface elements 902 and 903 to move one or more of the corresponding instrument interface elements 803 and 804 to drive one or more of the joints 507 and 513 such that the first end effector element 502 is not exerting a gripping force on the second end effector element 503. In some implementations, on receiving the signal from the input device, the control unit can move both of drive assembly interface elements 902 and 903 to move the corresponding instrument interface elements 803 and 804 to drive both of the joints 507 and 513 so that the first end effector element 502 is not exerting a gripping force on the second end effector element 503. The control unit may also be configured not to move drive assembly interface element 904, which drives joint 506, on receiving the signal. Therefore, the position of joint 506 may not change when one or more of the end effector elements 502, 503 moves from a respective first position to a respective second position so that the first end effector element 502 is not exerting a gripping force on the second end effector element 503 (and vice versa).

In other implementations, only one of the end effector elements may be moveable relative to the other end effector element. For example, joint 507 may permit the first end effector element 502 to rotate about the axis 512. The second end effector element 503 may in some implementations have a fixed position relative to supporting body 509. In some implementations, joint 506 may not be present and the end effector cannot rotate about an axis transverse to the longitudinal axis of the shaft 511.

In implementations where only one end effector element is moveable, the control unit may drive the drive assembly interface element corresponding to the end effector element that is moveable to cause the moveable end effector element to transition from a state in which it exerts a gripping force on the other, non-moveable end effector element to a state in which it does not exert a gripping force on the other end effector element. In such implementations, only the drive assembly interface element corresponding to the joint about which the moveable end effector element can move may be driven to move from its respective first position to its respective second position within the drive assembly interface.

For example, if only the first end effector element 502 is moveable about its joint 507, on receiving the signal from the input device, the control unit can move drive assembly interface element 902 to move instrument interface element 803 to a position where the first end effector element 502 is not exerting a gripping force on the second end effector element 503. The control unit can move drive assembly interface element 902 to move instrument interface element 803 to a position where the first end effector element 502 is in contact with the second end effector element 503 but is not exerting a gripping force on the second end effector element 503 (i.e. the jaws are closed but not gripping). In this case, the drive assembly interface element 903 is not used to drive a joint of the instrument and the control unit may be configured not to move drive assembly interface element 903 on receiving the signal. The control unit may also be configured not to move drive assembly interface element 904, which drives joint 506, on receiving the signal.

Therefore, one or more drive assembly interface elements which can be driven to control the spread of the end effector can be relaxed and the motion of the drive assembly interface elements can be made in such a way that the pitch and yaw of the instrument (for example motion about joint 506) does not change. This may avoid the end effector moving in a way that could injure the patient. This may also allow tissue that is being gripped by the end effector to be removed from between the jaws to minimize further damage to the tissue.

The control unit can determine that the first and second end effector elements are in contact but not exerting a griping force on one another (i.e. are not in an overclosed state) from the positions of the drive assembly interface elements in the drive assembly.

The drive assembly may comprise one or more position sensors configured to provide a respective position signal to the control unit indicating the position of a respective drive assembly interface element within the drive assembly. In the examples shown in Figures 6 to 8, there may be three such position sensors; one for each of the drive assembly interface elements 902, 903, 904. The position of the instrument can therefore be controlled by mapping the position of the drive assembly interface elements to the spread, pitch and yaw of the end effector. The mapping of the positions of the drive assembly interface elements to the position/state of the end effector elements may be stored in a memory at the control unit and may be used by the processor to allow it to move one or more of the drive assembly interface elements to their respective positions in which the first end effector element does not exert a gripping force on the second end effector element (and vice versa).

Therefore, in response to receiving the signal, the control unit can cause the drive assembly to drive one or more of the drive assembly interface elements 902, 903 to move from a respective first position to a respective second position. The respective first and second positions may be respective longitudinal positions along the drive assembly parallel to both the longitudinal axis of the terminal limb of the robot arm 908 and the longitudinal axis of the instrument shaft 808.

The respective first position of a drive assembly interface corresponds to a position in which the first end effector element is driven to exert gripping force on the second end effector element. The respective second position of a drive assembly interface element corresponds to a position in which the first end effector element is not driven to exert a gripping force on the second end effector element. The respective second position of a drive assembly interface element may correspond to a position in which the first end effector element is in contact with the second end effector element.

When a respective drive assembly interface element is driven to move from its respective first position to its respective second position, the respective end effector element associated with a respective drive assembly interface element is driven, via its respective instrument interface element and pair of driving elements, to move about its respective joint from a position in which the respective end effector element exerts a gripping force on the other end effector element to a position in which the respective end effector element does not exert a gripping force on the other end effector element, for example to a position in which the respective end effector element is in contact with the other end effector element but does not exert a gripping force on the other end effector element.

As mentioned above, the processor can be further configured to cause the drive assembly to drive the one or more joints to transition one or more of the end effector elements from a state in which it is gripping to a state in which it is not gripping (by moving the drive assembly interface elements associated with the end effector element(s)) in response to the processor receiving an indication of a fault. The fault may be a fault relating to a component of the surgical robotic system other than the robotic arm and/or the instrument. In some cases where a fault occurs with the robot arm or the instrument, the instrument may be automatically relaxed. However, where the fault occurs in other components of the system, such as the command interface, this may prevent a user from being able to control the joints of the instrument to be able to remove the instrument from the arm quickly and easily.

Therefore, the fault in the surgical robotic system may be a fault in one or more of a command interface (for example, a surgeon's console) remote from the robotic arm for allowing a surgeon to control the robotic arm, a further robotic arm of the surgical robotic system and an imaging device of the surgical robotic system.

The control unit may be further configured to cause the drive assembly to drive one or more of the drive assembly interface elements to move from its respective first position to its respective second position in response to the processor additionally receiving an indication of one or more of the following: 1) An indication that the robot arm carrying the instrument is in a normal mode of operation, for example not in a post-fault, fault-locked, or powering down mode. Power On Self Test (POST) is a series of self-tests each subsystem, such as the robot arm, performs on start-up. When a robot arm starts up with an alarm, usually it has failed one of these tests. These tests may test different components of the robot arm and check several things, such as that software versions are correct and that the joints are the correct revision. In post-fault mode, the processor of the control unit can instruct all joint controllers of the robot arm to autonomously hold the joints they control fixed at the position they were in on entry to the mode. The arm can be triggered into a fault-locked mode if the control unit detects a fault such as a clash, a position tracking error over a threshold, or other errors. If a fault is detected, the arm can produce an alarm and the processor can instruct the joint controllers to autonomously hold the joints fixed at the position they were in when the fault was triggered. In powering down mode, the processor switches off the arm back up battery and, if present, the battery of a moveable cart. The processor can also request that the joint and instrument drive motors are switched off. In these modes, the instrument may be relaxed anyway and so removal of the instrument may not be prevented.

2) An indication that any other robot arms in the surgical system have not been paused or subjected to an emergency shutdown procedure. For example, a robot arm carrying an endoscope for viewing of the surgical site during the surgical procedure.

3) An indication that an instrument is engaged with the robot arm that has two or more end effector elements, for example a first end effector element and a second end effector element, where at least one of the end effector elements is moveable relative to the other end effector element(s). For example, an indication that an instrument comprising a pair of jaws is engaged with the robot arm.

4) An indication that the instrument is being requested to 'overdose', i.e. one or more of the drive assembly interface elements are being driven to apply sufficient force to squeeze the first and second end effector elements together, whether or not there is something between the jaws.

When one or more of the above conditions are true and upon receiving the signal from an input device when a user inputs a request to disengage the instrument from the robot arm, the control unit can control the drive assembly of the robot arm to transition the instrument interface elements to the state which would leave the end effector closed but not gripping, to allow easier removal of the instrument from the robot arm.

In addition to the control unit causing movement of one or more of the drive assembly instrument interface elements, the control unit may be further configured to cause the following operations to occur upon receiving the signal in order to maintain a consistent user experience.

A robot arm may be temporarily moved to a disengaged state in which it cannot be controlled via command interface 312 while the user is engaging with the input device 313. The robot arm may not be moved back to the engaged state, in which it can be controlled via command interface 312, until the user is no longer engaging with the input device 313.

As mentioned above, the control unit may output a signal to allow an audible flag to be output by the surgical robotic system when a successful instrument disengagement request had been made. The surgical robotic system may routinely output audible flags when other operations have been completed. For example, the system may output different sounds when operations have been completed that result in a change of mode of the robot arm or the surgical robotic system. Different sounds may have different pitches and/or duration For example, a "Yes" sound can indicate a change of mode and a different "No" sound can indicate no change. The instrument disengagement request operation can maintain the convention that a "Yes" sound indicates a change of mode and a "No" sound indicates no change. Therefore, a successful instrument disengagement request may be followed by a "No" sound. Engagement with the input device 313 by a user for at least the predetermined time period may only cause a "Yes" sound if the robot arm transitions to an unlocked state (for example, when no instrument is attached).

A user engaging with input device 313 for more than the predetermined time period may also allow the joints of the robot arm to be moved. This may be beneficial in rare circumstances when two robot arms are clashing and may have the effect of allowing the robot arm to move to reduce the forces causing the clash. This may allow the VPP to be preserved.

The approach described herein can allow staff in an operating theatre to be able to control the robot to allow disengagement of the instrument when there is a fault in the surgical robotic system that results in the surgeon not being able to control the robot using the command interface console as normal. By making a request to disengage the instrument from the robot arm as described above, the interface elements on the drive assembly and the instrument can be relaxed to allow the instrument to be easily removed from the drive assembly.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention. As used herein, 'having' means 'comprising'.

Claims

CLAIMS1. A control unit for a surgical robotic system, the surgical robotic system comprising a robotic arm comprising a drive assembly having a first drive assembly interface element configured to provide mechanical drive for actuating a first joint of an instrument when the robotic arm engages with the instrument, the instrument having an end effector comprising a first end effector element and a second end effector element, the first end effector element being moveable with respect to the second end effector element about the first joint, the control unit being configured to control the drive assembly and comprising one or more processors configured to: receive a signal from an input device when a user inputs a request to disengage the instrument from the robotic arm; and in response to receiving the signal, cause the first drive assembly interface element to move from a first position in which the first end effector element exerts a gripping force on the second end effector element to a second position in which the first end effector element does not exert a gripping force on the second end effector element.
2. The control unit as claimed in claim 1, wherein in the second position the first end effector element is in contact with the second end effector element.
3. The control unit as claimed in claim 1 or claim 2, wherein the first drive assembly interface element is configured to drive a first instrument interface element of the instrument when the robotic arm engages the instrument.
4. The control unit as claimed in claim 3, wherein the first instrument interface element is connected to a first pair of driving elements for driving the first joint.
5. The control unit as claimed in any preceding claim, wherein the drive assembly comprises a guide constraining the displacement of the first drive assembly interface element within the drive assembly.
6. The control unit as claimed in any preceding claim, wherein the drive assembly comprises a position sensor configured to provide a position signal to the control unit indicating the position of the first drive assembly interface element within the drive assembly.
7. The control unit as claimed in any preceding claim, wherein the robotic arm extends between a base and a terminal limb, the terminal limb connected to an adjacent limb in the robotic arm by a joint which permits the terminal limb to rotate about a longitudinal axis of the terminal limb, the terminal limb comprising the drive assembly.
8. The control unit as claimed in claim 3 or claim 4 or as claimed in any of claims 5 to 7 as dependent on claim 3 or claim 4, wherein the first drive assembly interface element is engageable with the first instrument interface element on the longitudinal axis of the terminal limb, and wherein the first drive assembly interface element is linearly displaceable in a direction parallel to the longitudinal axis of the terminal limb so as to drive the first instrument interface element in a direction parallel to the longitudinal axis of the terminal limb.
9. The control unit as claimed in any preceding claim, wherein, at the time of the request to disengage the instrument from the robotic arm, the drive assembly is configured to drive the first joint such that the first end effector element exerts a gripping force on the second end effector element.
10. The control unit as claimed in any preceding claim, wherein the end effector further comprises a second joint about which the second end effector element is moveable with respect to the first end effector element.
11. The control unit as claimed in claim 10, wherein the drive assembly comprises a second drive assembly interface element configured to provide mechanical drive for actuating the second joint of the instrument when the robotic arm engages with the instrument.
12. The control unit as claimed in claim 11, wherein the one or more processors is/are further configured to, in response to receiving the signal, cause the second drive assembly interface element to move from a position in which the second end effector element exerts a gripping force on the first end effector element to a position in which the second end effector element does not exert a gripping force on the first end effector element.
13. The control unit as claimed in any preceding claim, wherein the instrument further comprises an articulation having a third joint about which the end effector can be driven to adopt a range of positions relative to a longitudinal axis of a shaft of the instrument.
14. The control unit as claimed in claim 13, wherein the drive assembly further comprises a third drive assembly interface element configured to drive a third instrument interface element of the instrument when the robotic arm engages the instrument, the third instrument interface element being connected to a third pair of driving elements for driving the third joint.
15. The control unit as claimed in claim 13 or claim 14, wherein the one or more processors is/are further configured to, in response to receiving the signal, not cause the drive assembly to drive the third joint.
16. The control unit as claimed in any preceding claim, wherein the robotic arm comprises the input device.
17. The control unit as claimed in any preceding claim, wherein the one or more processors is/are configured to receive the signal in response to the user engaging the input device for at least a predetermined time period.
18. The control unit as claimed in claim 17, wherein the predetermined time period is at least 1 second
19. The control unit as claimed in claim 18, wherein the one or more processors is/are configured to output one or more of an audible signal, a visual signal and a haptic signal when the user has engaged with the input device for at least the predetermined time period.
20. The control unit as claimed in preceding claim, wherein the first end effector element is a first jaw of a pair of jaws and the second end effector element is a second jaw of a pair of jaws.
21. The control unit as claimed in any preceding claim, wherein the surgical robotic system comprises one or more additional input devices configured to control the robotic arm and/or the instrument to perform a surgical procedure.
22. The control unit as claimed in any preceding claim, wherein the one or more processors is/are further configured to cause the first drive assembly interface element to move from the first position to the second position in response to the one or more processors receiving an indication of a fault.
23. The control unit as claimed in claim 22, wherein the fault is a fault relating to a component of the surgical robotic system other than the robotic arm and/or the instrument.
24. The control unit as claimed in claim 23, wherein the fault is a fault relating to one or more of a command interface remote from the robotic arm configured to allow a surgeon to control the robotic arm, a further robotic arm of the surgical robotic system and an imaging device of the surgical robotic system.
25. A surgical robot comprising: a robotic arm comprising a drive assembly having a first drive assembly interface element configured to provide mechanical drive for actuating a first joint of an instrument when the robotic arm engages with the instrument, the instrument having an end effector comprising a first end effector element and a second end effector element, the first end effector element being moveable with respect to the second end effector element about the first joint; and the control unit as claimed in any preceding claim.