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EP-4171420-B1 - CONTROLLING A SURGICAL INSTRUMENT

EP4171420B1EP 4171420 B1EP4171420 B1EP 4171420B1EP-4171420-B1

Inventors

  • VEITCH, Graham John
  • Webster-smith, David William Haydn
  • Glasscock, Roy Andrew

Dates

Publication Date
20260506
Application Date
20210628

Claims (16)

  1. A control system for controlling manipulation of a surgical instrument (304) in response to manipulation of a remote surgeon input device (600), the surgical instrument comprising opposable first and second end effector elements (209, 210) connected to a shaft (202) by an articulated coupling (203), the first and second end effector elements being rotatable in opposing rotational directions, the control system configured to: transform (805) commands from the surgeon input device to alter the opening angle between the first and second end effector elements according to a first control relationship to drive signals for driving the first and second end effector elements to rotate; receive (801) sensed forces applied to the first and second end effector elements, and compare (802) the sensed forces to a threshold force; and upon determining that the threshold force has been exceeded, transform (808) subsequent commands from the surgeon input device to alter the opening angle between the first and second end effector elements according to a second control relationship to drive signals for driving the first and second end effector elements to rotate, wherein the second control relationship is different to the first control relationship; characterised in that , under the same command from the surgeon input device to alter the opening angle between the first and second end effector elements, the control system is configured to: when the first control relationship is enabled, generate drive signals to drive the first and second end effector elements to rotate to an opening angle of θ according to the first control relationship, and when the second control relationship is enabled, generate drive signals to drive the first and second end effector elements to rotate according to the second control relationship to: an opening angle of θ + Δθ, where Δθ > 0, when the sensed forces are applied in a direction so as to close the first and second end effector elements together; or an opening angle of θ - Δθ, where Δθ > 0, when the sensed forces are applied in a direction so as to open the first and second end effector elements apart.
  2. A control system as claimed in claim 1, wherein the surgeon input device comprises two portions movable relative to each other, the first control relationship is a position control relationship, and the second control relationship is a position control relationship, where in a position control relationship the relative position of the two portions of the surgeon input device maps directly to the relative position of the first and second end effector elements of the surgical instrument.
  3. A control system as claimed in claim 1 or 2, wherein the opening angle between the first and second end effector elements is in a range bounded by a maximum opening angle θ max , and the threshold force is the received sensed force applied to the first and second end effector elements when (i) no external load is applied to the first and second end effector elements, and (ii) the opening angle between the first and second end effector elements is the maximum opening angle θ max .
  4. A control system as claimed in any preceding claim, wherein Δθ is calculated to match and thereby counteract the effective change in opening angle caused by the sensed forces acting on the end effector elements.
  5. A control system as claimed in any preceding claim, wherein Δθ is a function of the sensed forces.
  6. A control system as claimed in any preceding claim, wherein one or more motors are configured to drive the first and second end effector elements to rotate according to the drive signals, those one or more motors each capable of generating a maximum torque, wherein Δθ has a maximum value of Δθ max , where θ + Δθ max is the opening angle between the first and second end effector elements driven by the one or more motors at maximum torque when no external load is applied to the first and second end effector elements.
  7. A control system as claimed in any preceding claim, configured to model the driving of the first and second end effector elements as a spring, wherein Δθ is a function of a spring constant K e .
  8. A control system as claimed in any preceding claim, configured to provide a continuous mapping from the surgeon input device to the first and second end effector elements when transitioning from transforming commands from the surgeon input device according to the first control relationship to transforming subsequent commands from the surgeon input device according to the second control relationship.
  9. A control system as claimed in claim 8 when dependent on claims 3, 6 and 7, wherein Δ θ = min f e K e θ cont , Δ θ max wherein f e is an opening strain force between the first and second end effector elements derived from the received sensed forces, and θ cont is a function of the opening angle θ which provides the continuous mapping.
  10. A control system as claimed in any preceding claim, configured to only transform subsequent commands from the surgeon input device according to the second control relationship if the opening angle θ between the first and second end effector elements is greater than a baseline opening angle θ base .
  11. A control system as claimed in claim 10 when dependent on claim 9 when dependent on claim 3, wherein θ cont = θ − θ base θ max − θ base .
  12. A control system as claimed in claim 6 or any of claims 7 to 11 when dependent on claim 6, the surgical instrument being a robotic surgical instrument held and driven by a robotic surgical arm, the robotic surgical arm comprising an instrument drive configured to transfer drive from the one or more motors to the first and second end effector elements, wherein the sensed forces that the control system is configured to receive are measured at the instrument drive.
  13. A control system as claimed in claim 12 when dependent on claim 11 when dependent on claim 3, wherein the instrument drive comprises a first joint which transfers drive from a first motor of the one or more motors to rotation of the first end effector element, and a second joint which transfers drive from a second motor of the one or more motors to rotation of the second end effector element, wherein the opening strain force between the first and second end effector elements is: f e = max f sens − f d , 0 where f sens is a function of a force f 1 sensed at the first joint of the instrument drive and a force f 2 sensed at the second joint of the instrument drive, and f d is a received sensed force applied to the first and second end effector elements when (i) no external load is applied to the first and second end effector elements, and (ii) the opening angle between the first and second end effector elements is the maximum opening angle θ max .
  14. A control system as claimed in claim 13, configured to calculate f sens according to the equation f sens = f 1 + f 2 − f 1 base + f 2 base where f 1 base is a force sensed at the first joint of the instrument drive at a baseline opening angle θ base between the first and second end effector elements, and f 2 base is a force sensed at the second joint of the instrument drive at the baseline opening angle θ base between the first and second end effector elements.
  15. A control system as claimed in claim 13, configured to calculate f sens iteratively as a filtered version of Δ f = f 1 + f 2 − f 1 base + f 2 base according to the equation f sens n = α Δ f n + 1 − α f sens n − 1 where f 1 base is a force sensed at the first joint of the instrument drive at a baseline opening angle θ base between the first and second end effector elements, f 2 base is a force sensed at the second joint of the instrument drive at the baseline opening angle θ base between the first and second end effector elements, f sens n is f sens from the current iterative cycle, f sens n-1 is f sens from the previous iterative cycle, and α is a filter constant.
  16. A control system as claimed in claim 1, wherein one or both of the first control relationship and the second control relationship is a force control relationship, where in a force control relationship a force applied to the surgeon input device maps directly to a force applied to the first and second end effector elements of the surgical instrument.

Description

BACKGROUND It is known to use robots for assisting and performing surgery. Figure 1 illustrates a typical surgical robotic system. A surgical robot 100 consists of a base 102, an arm 104 and an instrument 106. The base supports the robot, and may itself be attached rigidly to, for example, the operating theatre floor, the operating theatre ceiling or a cart. The arm extends between the base and the instrument. The arm is articulated by means of multiple flexible joints 108 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 of the robot arm. The surgical instrument penetrates the body of the patient at a port so as to access the surgical site. The surgical instrument comprises a shaft connected to a distal end effector 110 by a jointed articulation. The end effector engages in a surgical procedure. In figure 1, the illustrated end effector is a pair of jaws. A surgeon controls the surgical robot 100 via a remote surgeon console 112. The surgeon console comprises one or more surgeon input devices 114. These may take the form of a hand controller or foot pedal. The surgeon console also comprises a display 116. A control system 118 connects the surgeon console 112 to the surgical robot 100. 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 104 and end effector 110. The control system sends these control signals to the robot, where the corresponding joints are driven accordingly. For example, the surgeon input device 114 may be a hand controller which has two portions moveable relative to each other, for example a trigger moveable relative to a body. The surgeon may move the trigger relative to the body to cause the jaws of the end effector 110 to open and close. Typically, the surgeon's movements are on a larger scale than the intended movement of the jaws. The control system transforms the inputs received from the hand controller to drive signals for driving the jaws to open or close according to a control relationship. That control relationship usefully scales the inputs from the hand controller so as to enable small and precise movements of the jaws in response to larger scale movement of the hand controller by the surgeon. The control relationship is generally such that movement of the trigger over its whole range of motion is mapped to movement of the opening angle between the jaws over its whole range from fully open to closed. In isolation, this enables the fine control of the jaws described above. However, in the presence of external forces applied to the jaws, such as from tissue surrounding the jaws at the surgical site, this delicate control may be insufficient to cause the desired movement of the jaws. Thus, there is a need for a control system which better converts inputs received from the surgeon input device(s) to control signals to move the end effector as desired in the presence of the external environment at the end effector. WO 2013/018935 relates to a surgical instrument having an end effector that is opened and closed and a control method thereof. US 10166082 relates to a system for controlling a surgical robotic tool having an end effector driven by actuators through antagonistic cables. US 2014/343569 relates to a teleoperated surgical system that includes a surgical instrument with an end effector and a master input device. SUMMARY OF THE INVENTION The invention is defined by appended independent claim, preferred embodiments are defined by appended dependent claims. According to an aspect of the disclosure, 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 opposable first and second end effector elements connected to a shaft by an articulated coupling, the control system configured to: transform commands from the surgeon input device to alter the opening angle between the first and second end effector elements according to a first control relationship to drive signals to drive the first and second end effector elements to rotate; receive sensed forces applied to the first and second end effector elements, and compare the sensed forces to a threshold force; and upon determining that the threshold force has been exceeded, transform subsequent commands from the surgeon input device to alter the opening angle between the first and second end effector elements according to a second control relationship to drive signals to drive the first and second end effector elements to rotate, wherein the second control relationship is different to the first control relationship. The surgeon input device may comprise two portions movable relative to each other. The first control relationship may be a position control relationship, and the second control relationship