Patent Description:
A control system <NUM> connects the surgeon console <NUM> to the surgical robot <NUM>. The control system receives inputs from the surgeon input device(s) and converts these to control signals to move the joints of the robot arm <NUM> and end effector <NUM>. The control system sends these control signals to the robot, where the corresponding joints are driven accordingly.

It is known for the jaws of an end effector to be individually driven by cables. These cables may be utilised to drive opening and closing of the jaws so as to grip and release an object between them. The same cables may also be used to drive a yawing motion of the jaws so as to cause the jaws to rotate in the same direction with the opening angle of the jaws remaining constant. Since the same cables are used to drive both the opening/closing and yawing motion of the jaws, these operations are not independent. As a result of this, the whole range of opening/closing motion cannot be accessed over the whole range of yawing motion, and vice versa.

Thus, there is a need for a control system which better mediates the interdependence of the opening/closing and yawing motion of an end effector.

<CIT> describes a method of controlling the movement of an end effector for performing surgical tasks in a space-constrained environment. The user can elect a reference point, such as an end effector element, to remain stationary when opening/closing the end effector elements relative to each other. <CIT> describes a method of using inverse kinematics to control a robotic system in response to receiving surgeon input, particularly as the tool approaches and/or passes through a singularity. Movement of the end effector may be limited in boundary zones around singularities so as to maintain the robot's degrees of freedom and prevent movement of the tool becoming unpredictable. <CIT> discloses a method of reengaging control of an instrument attached to a surgical robot arm using a surgeon input device following a period of disengagement. GB'<NUM> stages the reengagement of the surgeon input device by firstly engaging operative control of the surgical robot arm, and secondly engaging operative control of the instrument, so as to prevent any undesired movement of the end effector of the instrument upon reengagement.

According to the invention, there is provided a control system for controlling manipulation of a surgical instrument in response to manipulation of a remote surgeon input device, the surgical instrument comprising an end effector having opposable first and second end effector elements connected to a shaft by an articulated coupling, the control system configured to: receive a command from the surgeon input device to both (i) change the orientation of the end effector, and (ii) open the first and second end effector elements relative to each other; in response to the command to change the orientation of the end effector, determine an angle θ between the longitudinal axis of the articulated coupling and the end effector; in response to the command to open the first and second end effector elements, determine an opening angle φ between the first and second end effector elements; compare θ to a maximum angle θmax between the longitudinal axis of the articulated coupling and the end effector; and if θ > θmax, drive the first and second end effector elements to rotate such that (i) the angle between the longitudinal axis of the articulated coupling and the end effector is θmax, and (ii) the opening angle between the first and second end effector elements is φ.

The control system may be configured to determine the opening angle φ between the first and second end effector elements by: in response to the command to open the first and second end effector elements, determine an opening angle ψ; compare ψ to a maximum angle φmax between the first and second end effector elements; and if ψ > φmax, drive the first and second end effector elements to rotate such that the opening angle between the first and second end effector elements φ = φmax.

The control system may be configured to, if ψ ≤ φmax, drive the first and second end effector elements to rotate such that the opening angle between the first and second end effector elements φ = ψ.

The command from the surgeon input device to change the orientation of the end effector may comprise a rotation of at least a portion of the surgeon input device in its workspace.

The surgeon input device may comprise a body and a trigger, and the command from the surgeon input device to open the first and second end effector elements relative to each other may comprise a movement of the trigger relative to the body.

The command from the surgeon input device to open the first and second end effector elements relative to each other may comprise a rotation of the trigger away from the body.

The angle between the trigger and the body at the end of the rotation may be proportional to φ.

The command from the surgeon input device to open the first and second end effector elements relative to each other may comprise a linear translation of the trigger relative to the body.

The articulated coupling may comprise a first joint driveable by a first pair of driving elements, and a second joint driveable by a second pair of driving elements. The control system may be configured to drive the first and second end effector elements to rotate by: commanding a first force to be applied to the first pair of driving elements so as to cause the first end effector element to rotate about the first joint; and commanding a second force to be applied to the second pair of driving elements so as to cause the second end effector element to rotate about the second joint.

The articulated coupling may further comprise a third joint driveable by a third pair of driving elements. The control system may be configured to: in response to the command to change the orientation of the end effector, determine an angle Ω between the longitudinal axis of the shaft and the articulated coupling; and drive the end effector to rotate about the third joint by Ω.

The control system may be configured to drive the end effector to rotate about the third joint by commanding a third force to be applied to the third pair of driving elements so as to cause the end effector to rotate about the third joint.

The control system may be configured to: following driving the first and second end effector elements to rotate such that the angle between the longitudinal axis of the articulated coupling and the end effector is θmax, receive a further command from the surgeon input device to increase the opening angle between the first and second end effector elements relative to each other; in response to the further command: determine an opening angle φ' between the first and second end effector elements; determine an angle θmax' between the longitudinal axis of the articulated coupling and the end effector, where θmax' is a function of φ'; and drive the first and second end effector elements to rotate such that (i) the angle between the longitudinal axis of the articulated coupling and the end effector is θmax', and (ii) the opening angle between the first and second end effector elements is φ'.

Optionally, θmax' = αmax - φ'/<NUM>, where αmax is the maximum rotation from the longitudinal axis of the articulated coupling of the end effector element in the commanded direction of rotation.

Each of the first and second pairs of driving elements may comprise cables.

The first force, second force and/or third force may be tension forces.

The opposable first and second end effector elements may be one of: a pair of jaws, a pair of scissors, and a needle driver.

The invention is disclosed by appended independent claim <NUM>, preferred embodiments being disclosed by appended dependent claims.

The following describes controlling a surgical robotic instrument from a remote surgeon console. The instrument and console form part of a surgical robotic system of the type illustrated in <FIG>.

The surgical instrument is supported by a robot arm. The robot arm is itself supported by a base. During surgery, the base is secured to part of the operating theatre, for example the floor, ceiling, cart or patient bed. The robot arm remains at all times external to the patient. The robot arm comprises a series of arm links interspersed with joints. These joints may be revolute joints. The end of the robot arm distal to the base can be articulated relative to the base by movement of one or more of the joints. The surgical instrument attaches to a drive assembly at the distal end of the robot arm. This attachment point is external to the patient. The surgical instrument has an elongate profile, with a shaft spanning between its proximal end which attaches to the robot arm and its distal end which accesses the surgical site within the patient body. The proximal end of the surgical instrument and the instrument shaft may be rigid with respect to each other and rigid with respect to the distal end of the robot arm when attached to it. An incision is made into the patient body, through which a port is inserted. The surgical instrument may penetrate the patient body through the port to access the surgical site. Alternatively, the surgical instrument may penetrate the body through a natural orifice of the body to access the surgical site. At the proximal end of the instrument, the shaft is connected to an instrument interface. The instrument interface engages with the drive assembly at the distal end of the robot arm. Specifically, individual instrument interface elements of the instrument interface engage individual drive assembly interface elements of the drive assembly. The instrument interface is releasably engageable with the drive assembly. The instrument can be detached from the robot arm manually without requiring any tools. This enables the instrument to be detached from the drive assembly quickly and another instrument attached during an operation.

At the distal end of the surgical instrument, the shaft is connected to an end effector by an articulated coupling. The end effector engages in a surgical procedure at the surgical site. <FIG> and <FIG> illustrate the distal end of an exemplary instrument which has a pair of jaws as the end effector <NUM>. The shaft <NUM> is connected to the end effector <NUM> by articulated coupling <NUM>. The articulated coupling <NUM> comprises several joints. These joints enable the pose of the end effector to be altered relative to the direction of the instrument shaft. Although not shown in <FIG> and <FIG>, the end effector may also comprise joint(s). In the example of <FIG> and <FIG>, the articulated coupling <NUM> comprises a pitch joint <NUM>. The pitch joint <NUM> rotates about pitch axis <NUM>, which is perpendicular to the longitudinal axis <NUM> of the shaft <NUM>. The pitch joint <NUM> permits a supporting body <NUM> (described below) and hence the end effector <NUM> to rotate about the pitch axis <NUM> relative to the shaft. In the example of <FIG> and <FIG>, the articulated coupling also comprises a first yaw joint <NUM> and a second yaw joint <NUM>. First yaw joint <NUM> rotates about first yaw axis <NUM>. Second yaw joint <NUM> rotates about second yaw axis <NUM>. Both yaw axes <NUM> and <NUM> are perpendicular to pitch axis <NUM>. Yaw axes <NUM> and <NUM> may be parallel. Yaw axes <NUM> and <NUM> may be collinear. The articulated coupling <NUM> comprises a supporting body <NUM>. At one end, the supporting body <NUM> is connected to the shaft <NUM> by pitch joint <NUM>. At its other end, the supporting body <NUM> is connected to the end effector <NUM> by the yaw joints <NUM> and <NUM>. This supporting body is omitted from <FIG> for ease of illustration so as to enable the other structure of the articulated coupling to be more easily seen. The end effector <NUM> comprises two end effector elements <NUM>, <NUM>. The end effector elements shown are opposing jaws. However, the end effector elements may be any type of opposing end effector elements, further examples of which are discussed later. The first yaw joint <NUM> is fast with the first end effector element <NUM> and permits the first end effector element <NUM> to rotate about the first yaw axis <NUM> relative to the supporting body <NUM> and the pitch joint <NUM>. The second yaw joint <NUM> is fast with the second end effector element <NUM> and permits the second end effector element <NUM> to rotate about the second yaw axis <NUM> relative to the supporting body <NUM> and the pitch joint <NUM>.

The joints illustrated in <FIG> and <FIG> are driven by pairs of driving elements. The driving elements are elongate. They are flexible transverse to their longitudinal extent. They resist compression and tension forces along their longitudinal extent. Each pair of driving elements is secured at the other end of the instrument shaft to a respective instrument interface element 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 one or more joints of the articulation and/or end effector which moves the end effector. The driving elements may be cables. The driving elements may comprise flexible portions and a rigid portion. Flexible portions engage the components of the instrument interface and the articulated coupling, and the rigid portion extends through all or part of the instrument shaft. For example, the flexible portion may be a cable, and the rigid portion may be a spoke. Other rigid portion(s) may be in the instrument interface or articulated coupling of the instrument. For example, rack and pinions may be in the instrument interface or articulated coupling of the instrument.

<FIG> and <FIG> illustrate a first pair of driving elements A1, A2 which are constrained to move around the first yaw joint <NUM>. Driving elements A1, A2 drive rotation of the first end effector element <NUM> about the first yaw axis <NUM>. <FIG> and <FIG> illustrate a second pair of driving elements B1, B2 which are constrained to move around the second yaw joint <NUM>. Driving elements B1, B2 drive rotation of the second end effector element <NUM> about the second yaw axis <NUM>. <FIG> and <FIG> also illustrate a third pair of driving elements C1, C2 which are constrained to move around pitch joint <NUM>. Driving elements C1, C2 drive rotation of the end effector <NUM> about the pitch axis <NUM>. The end effector <NUM> can be rotated about the pitch axis <NUM> by applying tension to driving elements C1 and/or C2. The pitch joint <NUM> and yaw joints <NUM>, <NUM> are independently driven by their respective driving elements.

The end effector elements <NUM> and <NUM> are independently rotatable. The end effector elements can be rotated in opposing rotational directions. For example, the end effector elements can be rotated in opposing rotational directions towards each other by applying tension to driving elements A2 and B1. This closes the end effector elements together, which is useful for (i) gripping an object between the end effector elements, such as tissue or a needle or thread, and/or (ii) cutting an object between the end effector elements, such as tissue or thread. The end effector elements can be rotated in opposing rotational directions away from each other by applying tension to driving elements A1 and B2. This opens the end effector elements, which is useful for (i) releasing an object which has been grasped between the end effector elements, and/or (ii) reopening a pair of scissor end effector elements ready for another cutting action. Both end effector elements can be rotated in the same rotational direction, by applying tension to driving elements A1 and B1 or alternatively A2 and B2. This causes the end effector elements to yaw about the pivot axes <NUM> and <NUM>. This is useful for enabling the end effector to access a different part of the surgical site. Alternatively, one end effector element can be rotated (in either rotational direction) whilst the other end effector element is maintained in position, by applying tension to only one of driving elements A1, A2, B1, B2. Thus, both a gripping motion and a yawing motion of the end effector are enabled by manipulating the same pairs of driving elements: A1, A2 for the first end effector element <NUM>, and B1, B2 for the second end effector element <NUM>.

Any type of instrument having opposable end effector elements is relevant to the following description. A first exemplary type is cutting instruments, for which the end effector elements engage so as to cut tissue or another object between the end effector elements. A second exemplary type is gripping instruments, for which the end effector elements engage so as to grasp tissue or another object between the end effector elements.

The surgeon console comprises one or more surgeon input devices. Each surgeon input device enables the surgeon to provide a control input to the control system. A surgeon input device may, for example, be a hand controller, a foot controller such as a pedal, a touch sensitive input to be controlled by a finger or another part of the body, a voice control input device, an eye control input device or a gesture control input device. The surgeon input device may provide several inputs which the surgeon can individually operate.

<FIG> illustrates an exemplary hand controller <NUM>. The hand controller is connected to the surgeon console, for example by a gimbal arrangement (not shown). This enables the hand controller to be moved with three degrees of translational freedom with respect to the surgeon console. The hand controller shown is intended to be held by a right hand. A mirror image hand controller could be held by a left hand. The hand controller comprises a body <NUM> suitable for being gripped by a hand. The hand controller may comprise additional inputs, for example buttons, switches, levers, slide inputs or capacitive sensor inputs such as track pads <NUM>. The hand controller of <FIG> comprises a trigger <NUM>. The trigger <NUM> is movable relative to the body <NUM>. In the hand controller shown, the trigger <NUM> is rotatable relative to the body <NUM>. Alternatively, or in addition, the trigger could translate linearly relative to the body <NUM>. The hand controller may comprise two triggers, each trigger for independently controlling a single different one of the end effector elements <NUM>, <NUM>.

The surgeon may rotate the trigger <NUM> relative to the body <NUM> of the hand controller in order to command the end effector elements <NUM>, <NUM> of the instrument to close in a gripping/closing motion or to open in a releasing/opening motion. For example, the surgeon may rotate the trigger <NUM> towards the body <NUM> of the hand controller to command a gripping/closing motion. The surgeon may rotate the trigger <NUM> away from the body <NUM> of the hand controller to command a releasing/opening motion. The surgeon may rotate the body of the hand controller in the hand controller workspace to command a change in orientation of the end effector elements.

A control system connects the surgeon console to the surgical robot. The control system comprises a processor and a memory. The memory stores, in a non-transient way, software code that can be executed by the processor to cause the processor to control the surgeon console and robot arm and instrument in the manner described herein. The control system receives the inputs from the surgeon input device(s) and converts these to control signals to move the joints of the robot arm and/or the joint(s) of the articulated coupling and/or the joint(s) of the end effector. The control system sends these control signals to the robot arm, where the corresponding joints are driven accordingly. Manipulation of the surgical instrument is thereby controlled by the control system in response to manipulation of the surgeon input device.

When the control system is controlling an instrument having opposable end effector elements, on detecting an opening motion of the hand controller, the control system responds by commanding a force to be applied to the driving elements of the end effector elements to cause the end effector elements to rotate in opposing rotational directions away from each other. Referring to <FIG> and <FIG>, the control system responds to detecting the opening motion by commanding a force to be applied to A1 and a force to be applied to B2, thereby causing the end effector elements to spread apart.

On detection of a second motion of the hand controller in the hand controller workspace, the control system may respond by commanding articulation of any one or combination of: (i) the joints of the surgical robot arm, (ii) the joints of the articulated coupling <NUM> of the surgical instrument, and (iii) the joints of the end effector. This commanded articulation causes the pose of the end effector to change as directed by the second motion. For example, the second motion may be a rotation of the body <NUM> of the hand controller. As another example, the second motion may be manipulation of a further input on the hand controller, for example movement of a further trigger. That movement may be a rotation of the further trigger relative to the body of the hand controller. Alternatively, or in addition, the further trigger could translate linearly relative to the body <NUM>.

Thus, the control system may respond to detection of the second motion (such as rotation) of the body of the hand controller by, at least in part, commanding forces to be applied to the driving elements of the end effector elements to cause the end effector elements to rotate. For example, referring to <FIG> and <FIG>, the control system may command forces to be applied to A2 and B2 to cause the end effector elements <NUM> and <NUM> to yaw in a clockwise direction. The control system may command forces to be applied to A1 and B1 to cause the end effector elements <NUM> and <NUM> to yaw in an anti-clockwise direction. The control system may command the same force to be applied to both A1 and B1 (or A2 and B2). If the end effector elements match, and the driving elements for those end effector elements match, then for a configuration in which the end effector elements are not fully closed and exerting a forces against each other, applying the same force to both A1 and B1 (or A2 and B2) causes both end effectors elements to yaw in unison. The control system may also respond to detection of the second motion (such as rotation) of the body of the hand controller by commanding forces to be applied to one of C1 and C2 to cause a rotation of the pitch joint <NUM>. The control system may also respond to detection of the second motion (such as rotation) of the body of the hand controller by commanding torques to be applied about one or more of the joints of the robot arm.

The same driving elements A1, A2 and B1, B2 are utilised to drive rotation of the end effector elements for both opening and closing the end effector elements relative to each other and yawing the end effector. Thus, the opening/closing and yawing operations are not independently driven.

Referring to <FIG>, each end effector element <NUM>, <NUM> is capable of rotating about the axis of its connected joint <NUM>, <NUM> with respect to the longitudinal axis <NUM> of the articulated coupling <NUM>. The longitudinal axis <NUM> of the end effector element furthest from the longitudinal axis <NUM> of the articulated coupling <NUM> is depicted in <FIG> as being separated from the longitudinal axis <NUM> of the articulated coupling <NUM> by an angle α. The longitudinal axis <NUM> of the end effector element closest to the longitudinal axis <NUM> of the articulated coupling <NUM> is depicted in <FIG> as being separated from the longitudinal axis <NUM> of the articulated coupling <NUM> by an angle β. The end effector elements are separated by a spread of φ. In other words, the angle between the longitudinal axes <NUM> and <NUM> of the end effector elements is φ.

Each end effector element is limited in how far it can rotate about the axis of its connected joint. The maximum rotational angle between the longitudinal axis <NUM> of the furthest end effector and the longitudinal axis <NUM> of the articulated coupling <NUM> is αmax. For example, αmax may be in the range <NUM>° to <NUM>°. αmax may be in the range <NUM>° to <NUM>°. αmax may be <NUM>°. αmax may be instrument dependent. The end effector elements may be opened to a spread angle φ, and then yawed clockwise as shown in <FIG>. As the end effector elements yaw, the opening angle φ is initially maintained. However, once the furthest end effector element <NUM> reaches its rotation limit at an angle of αmax it stops rotating. If the surgeon input device continues to command a yawing action, and the control system continues to drive the instrument accordingly, then the end effector element <NUM> remains still, but the other end effector element <NUM> continues to yaw, i.e. continues to rotate clockwise. Thus, the opening angle φ starts to decrease, and hence the end effector elements start to close, even though the surgeon input device is still commanding the end effector elements to remain open.

In <FIG>, the end effector is illustrated as having yawed in a clockwise direction relative to the longitudinal axis <NUM> of the articulated coupling. End effector element <NUM> is thus furthest from the longitudinal axis <NUM> of the articulated coupling. The maximum rotation angle between the axes <NUM> and <NUM> is αmax. When the end effector yaws in an anticlockwise direction relative to the longitudinal axis <NUM> of the articulated coupling, then the end effector element <NUM> is furthest from the longitudinal axis <NUM> of the articulated coupling. In this scenario, the maximum rotational angle between the axes <NUM> and <NUM> is αmax. The maximum rotation angle αmax may be the same for both a clockwise rotation of one end effector element and an anticlockwise rotation of the other end effector element. This may be the case for symmetrical instruments. For other instruments, the maximum rotation angle αmax may be different for a clockwise rotation of one end effector element and an anticlockwise rotation of the other end effector element. For example, this may be the case for asymmetrical instruments. For some asymmetrical instruments, the end effector elements may have a range of motion which is restricted to one side only of the longitudinal axis <NUM> of the articulated coupling. In this scenario, the same end effector element is always furthest from the longitudinal axis <NUM> of the articulated coupling.

The end effector elements may also be limited in how far they can rotate away from each other. For example, the opening angle may be limited to φmax. φmax may be instrument dependent. For example, φmax may be in the range <NUM>° to <NUM>°. φmax may be in the range <NUM>° to <NUM>°.

<FIG> illustrates a method implemented by the control system to limit the yawing motion of the end effector so as to prioritise maintenance of the opening angle of the end effector elements.

At step <NUM> of <FIG>, the control system receives a command from the surgeon input device to both (i) change the orientation of the end effector, and (ii) open the end effector elements relative to each other.

As described above, the command from the surgeon input device to change the orientation of the end effector may be a rotation of the surgeon input device in its workspace. The surgeon input device may be connected to the surgeon console by an articulated linkage, optionally including a gimbal assembly. A position sensor may be included on each movable joint of the articulated linkage. The control system receives the sensed positions of each joint of the articulated linkage. From the known order, masses and lengths of the links and joints in the articulated linkage, and the received sensed positions, the control system determines the change of orientation of the surgeon input device. From the change of orientation of the surgeon input device, the control system determines the commanded change of orientation of the end effector.

The command from the surgeon input device to open the end effector elements relative to each other may be a rotation of the trigger away from the body of the surgeon input device. Alternatively, a command from the surgeon input device to open the end effector elements relative to each other may be a linear translation of the trigger relative to the body. For example, the hand controller <NUM> of <FIG> may include a position sensor which senses the rotational (or linear) position of the trigger <NUM> relative to the body <NUM> of the hand controller. The control system receives the sensed rotational (or linear) position of the trigger from the position sensor.

At step <NUM>, in response to the command to change the orientation of the end effector, the control system determines an angle θ between the longitudinal axis of the articulated coupling and the end effector. <FIG> illustrates θ as between the longitudinal axis <NUM> of the articulated coupling and an axis <NUM> which bisects the end effector elements. In <FIG>, the bisecting axis <NUM> is such that (i) axes <NUM>, <NUM> and <NUM> all intersect at a point, and (ii) the angle between the axes <NUM> and <NUM> is equal to the angle between the axes <NUM> and <NUM>. The axes <NUM>, <NUM> and <NUM> intersect where they meet the yaw axes <NUM> and <NUM>.

The angle θ is that determined to effect the change in orientation commanded by the surgeon input device. The angle θ may be proportional to the angle through which the surgeon input device has rotated in its workspace. In the case that a change in orientation is commanded by motion of part of the surgeon input device, such as a further trigger, then the angle θ may be proportional to the angle through which that part of the surgeon input device has rotated, or the distance along which that part of the surgeon input device has linearly translated.

At step <NUM>, the control system compares θ to θmax. θmax is the maximum value of θ. In other words, θmax is the maximum angle between the longitudinal axis <NUM> of the articulated coupling and the end effector. θmax may be a function of the opening angle of the end effector elements φ. Alternatively, or additionally, θmax may be a function of the maximum rotational angle αmax of the furthest end effector element. For example, <MAT>.

The control system determines whether θ > θmax. If θ ≤ θmax, then controlling the end effector elements to rotate such that the angle between the longitudinal axis <NUM> of the articulated coupling and the end effector is θ will not cause the opening angle of the end effector elements to start closing. Thus, if θ ≤ θmax, then at step <NUM>, the control system drives the first and second end effector elements to rotate such that the angle between the longitudinal axis <NUM> of the articulated coupling and the end effector is θ. For example, the angle between the longitudinal axis <NUM> of the articulated coupling and the bisecting axis <NUM> is θ.

If, at step <NUM>, the control system determines that θ > θmax, then controlling the end effector elements to rotate such that the angle between the longitudinal axis <NUM> of the articulated coupling and the end effector is θ will cause the opening angle of the end effector elements to start closing. Thus, instead, at step <NUM>, the control system drives the first and second end effector elements to rotate such that the angle between the longitudinal axis <NUM> of the articulated coupling and the end effector is θmax. For example, the angle between the longitudinal axis <NUM> of the articulated coupling and the bisecting axis <NUM> is θmax.

Meanwhile, the control system determines to drive an opening angle φ between the first and second end effector elements. At step <NUM>, in response to the command to open the end effector elements, the control system determines an opening angle ψ between the first and second end effector elements. Specifically, ψ is the angle between the longitudinal axis of the first end effector element <NUM> and the longitudinal axis of the second end effector element <NUM>. The angle ψ is that determined to effect the opening angle between the end effector elements commanded by the surgeon input device. The angle ψ may be proportional to the rotational position of the trigger relative to the body of the surgeon input device once the trigger has been moved to effect the command of step <NUM>.

At step <NUM>, the control system compares ψ to φmax. The control system determines whether ψ > φmax. If ψ ≤ φmax, then at step <NUM>, the control system drives the first and second end effector elements to rotate such that the angle between the longitudinal axes <NUM> and <NUM> of the end effector elements φ = ψ.

If at step <NUM>, the control system determines that ψ > φmax, then at step <NUM>, the control system drives the first and second end effector elements to rotate such that the angle between the longitudinal axes <NUM> and <NUM> of the end effector elements φ = φmax.

On <FIG>, steps <NUM>, <NUM>, <NUM> and <NUM> are all encased within a dashed step <NUM>. This is to indicate that those ones of steps <NUM>, <NUM>, <NUM> and <NUM> which are implemented in a given iteration of the control method of <FIG> are done so in concert. For example, If the answer to both steps <NUM> and <NUM> is NO, then steps <NUM> and <NUM> are performed in concert. If the answer to both steps <NUM> and <NUM> is YES, then steps <NUM> and <NUM> are performed in concert. If the answer to step <NUM> is NO and the answer to step <NUM> YES, then steps <NUM> and <NUM> are performed in concert. If the answer to step <NUM> is YES and the answer to step <NUM> NO, then steps <NUM> and <NUM> are performed in concert.

Performed in concert means that the control system determines the forces to be applied to the first pair of driving elements A1, A2 and the forces to be applied to the second pair of driving elements B1, B2 so as to cause both (i) the end effector to be driven to θ or θmax, and (ii) the opening angle to be driven to φ (i.e. ψ or φmax).

In response to the command to change the orientation of the end effector, the control system may also determine an angle Ω between the longitudinal axis <NUM> of the shaft <NUM> and the longitudinal axis <NUM> of the articulated coupling <NUM>. The angles θ and Ω are determined to together effect the change in orientation commanded by the surgeon input device. For example, the combined angle θ+Ω may be proportional to the angle through which the surgeon input device has been rotated in its workspace. In this scenario, at step <NUM>, the control system drives the third pair of driving elements C1, C2 so as to cause the supporting body <NUM> and hence the end effector <NUM> to rotate about the pitch axis <NUM> by the angle Ω.

After the end effector elements and/or supporting body have been driven to the angles described with reference to step <NUM>, the control loop may repeat. In other words, a further command may be received by the control system to change the orientation of the end effector and open the end effector elements at step <NUM>. In this case, the method described above repeats. Alternatively, a further command may be received by the control system to increase the opening angle between the end effector elements at step <NUM>. For example, the trigger of the surgeon input device may have been rotated further away from the body of the surgeon input device. No command is received from the surgeon input device to change the orientation of the end effector. If at step <NUM>, the end effector had been driven to θmax, then the furthest end effector element <NUM> is already at the maximum rotation angle αmax that it can sustain at the current opening angle of φ.

In response to the further command at step <NUM>, at step <NUM> the control system determines φ'. φ' is an opening angle between the first and second end effector elements. φ' is determined to effect the opening angle between the end effector elements commanded by the surgeon input device at step <NUM>. The angle φ' may be proportional to the rotational position of the trigger relative to the body of the surgeon input device once the trigger has been moved to effect the command of step <NUM>.

Then, at step <NUM>, the control system determines θmax'. θmax' is the maximum angle between the longitudinal axis of the articulated coupling and the end effector which enables the opening angle φ' to be sustained. θmax' may be a function of the opening angle of the end effector elements φ'. Alternatively, or additionally, θmax' may be a function of the maximum rotational angle αmax of the furthest end effector element. For example, <MAT>.

Then, at step <NUM>, the control system drives the end effector elements to rotate such that (i) the angle between the longitudinal axis of the articulated coupling and the end effector is θmax', and (ii) the opening angle between the first and second end effector elements is φ'. Thus, in practice, the furthest end effector element <NUM> maintains its rotational position at αmax, and the closest end effector element <NUM> is driven to rotate towards the longitudinal axis of the articulated coupling <NUM>, thereby achieving the desired opening angle φ'.

As a numerical example, consider a case where αmax = <NUM>°. At step <NUM>, the opening angle of the end effector elements is driven to φ = <NUM>°. Thus, using equation <NUM>, θmax = <NUM>°. At step <NUM>, the end effector is driven to θmax = <NUM>°. Thus, the individual end effector elements are at <NUM>° and <NUM>° to the longitudinal axis <NUM> of the articulated coupling. At step <NUM>, the control system receives a command from the surgeon input device to open the end effector elements to an opening angle of φ' = <NUM>°. Since αmax = <NUM>°, using equation <NUM>, θmax' = <NUM>°. Thus, the individual end effector elements are at <NUM>° and <NUM>° to the longitudinal axis <NUM> of the articulated coupling.

Thus, the control method of <FIG> prevents the opening angle φ of the end effector elements from decreasing as the surgeon input device commands an increased yawing motion of the end effector. Maintaining the opening angle φ of the end effector elements is prioritised over maximising the angle from the longitudinal axis <NUM> of the articulated coupling to which each individual end effector element can rotate.

The steps illustrated in the control method of <FIG> are those relevant to the problem addressed herein. The control system performs many other steps during the control method of <FIG>. Those other steps are not shown in <FIG>.

The end effector may take any suitable form. For example, the end effector could be a pair of curved scissors, an electrosurgical instrument such as a pair of monopolar scissors, a needle holder, a pair of jaws, or a fenestrated grasper.

Claim 1:
A control system for controlling manipulation of a surgical instrument in response to manipulation of a remote surgeon input device, the surgical instrument comprising an end effector (<NUM>) having opposable first and second end effector elements (<NUM>, <NUM>) connected to a shaft (<NUM>) by an articulated coupling (<NUM>), the control system configured to:
receive a command from the surgeon input device to both (i) change the orientation of the end effector (<NUM>), and (ii) open the first and second end effector elements (<NUM>,<NUM>) relative to each other;
in response to the command to change the orientation of the end effector (<NUM>), determine an angle θ between the longitudinal axis (<NUM>) of the articulated coupling (<NUM>) and the end effector (<NUM>);
in response to the command to open the first and second end effector elements (<NUM>,<NUM>), determine an opening angle φ between the first and second end effector elements (<NUM>,<NUM>);
the control system characterised by, comparing θ to a maximum angle θmax between the longitudinal axis (<NUM>) of the articulated coupling (<NUM>) and the end effector (<NUM>), wherein θmax is a function of φ and αmax, αmax being the maximum rotation angle between the longitudinal axis (<NUM>) of the articulated coupling (<NUM>) and the end effector element furthest from the longitudinal axis (<NUM>) of the articulated coupling (<NUM>); and
if θ > θmax, drive the first and second end effector elements (<NUM>,<NUM>) to rotate such that (i) the angle between the longitudinal axis (<NUM>) of the articulated coupling (<NUM>) and the end effector (<NUM>) is θmax, and (ii) the opening angle between the first and second end effector elements (<NUM>, <NUM>) is φ.