Flexible instruments for a snake-like robot
File(s)
Author(s)
Schmitz, Andreas
Type
Thesis
Abstract
Minimally Invasive Surgery (MIS) is a widely adopted technique
due to the many advantages it holds for patients, e.g., reductions in
healing times. In MIS one procedure within many is using a snakelike robot for scarless endoscopic surgery, such as gastrointestinal
endoscopic surgery. In this type of surgery, the snake-like robot is
inserted through a natural orifice and is directed towards a chosen
surgical site. Once the robot is in place, small robotic instrument
arms are deployed from the head of the robot to perform surgical
tasks, e.g., cutting or suturing. These instruments need to have
a small diameter of approximately ⌀3-4mm such that they can
be inserted through working channels or biopsy ports within the
snake-like robot. Multiple designs of surgical instruments have been
proposed in research, such as concentric tube robots, soft robots or rigid-links tendonactuated robots. On the instrument tips grippers to hold the tissue, small scissors, or
knives can be mounted. Other more special types of instruments are available as well.
Surgeons can control the instruments remotely and see them through a camera which is
mounted on the tip of the robot.
This thesis is part of the the i2Snake project which developed a homonymous snake-like
robot with a length of 36.6cm and a diameter of 16mm. The length can be adapted by
adjusting the length of the passive part to adapt to different procedures. In the scope
of this thesis robotic instrument arms for the i2Snake robot were developed. Prototypes
of these arms were built with a diameter of ⌀4mm and ⌀3mm. Similar instruments
with a diameter of ⌀5mm and above were published before. For the new prototypes a
rolling gear joint was developed to improve the accuracy of the arm and a gripper with
an embedded distal roll. A shape sensor prototype was developed which only needs 3
receiving fibers. The 3mm instrument was optimised with a newly developed optimisation algorithm. To combine the developed approaches, a control was implemented which
incorporates a reinforcement learning inverse kinematics and a mathematical model to
compensate for backlash and joint coupling. The 4mm instrument with 7 DOF can bend
up to 72° in each joint and has a rolling motion of 165.65°. The final 3mm instrument
has 5 DOF, including a prismatic joint, and can bend up to 82° in each joint and roll
5for 90°. The learned inverse kinematics is more precise in position and orientation error
than the common Damped least-squares Jacobian pseudo-inverse, mainly because it has
no problems with joint limits or complex situations. Using the proposed compensation
methods, the backlash was significantly reduced so that the overall average positioning
error was improved to 1.49mm.
due to the many advantages it holds for patients, e.g., reductions in
healing times. In MIS one procedure within many is using a snakelike robot for scarless endoscopic surgery, such as gastrointestinal
endoscopic surgery. In this type of surgery, the snake-like robot is
inserted through a natural orifice and is directed towards a chosen
surgical site. Once the robot is in place, small robotic instrument
arms are deployed from the head of the robot to perform surgical
tasks, e.g., cutting or suturing. These instruments need to have
a small diameter of approximately ⌀3-4mm such that they can
be inserted through working channels or biopsy ports within the
snake-like robot. Multiple designs of surgical instruments have been
proposed in research, such as concentric tube robots, soft robots or rigid-links tendonactuated robots. On the instrument tips grippers to hold the tissue, small scissors, or
knives can be mounted. Other more special types of instruments are available as well.
Surgeons can control the instruments remotely and see them through a camera which is
mounted on the tip of the robot.
This thesis is part of the the i2Snake project which developed a homonymous snake-like
robot with a length of 36.6cm and a diameter of 16mm. The length can be adapted by
adjusting the length of the passive part to adapt to different procedures. In the scope
of this thesis robotic instrument arms for the i2Snake robot were developed. Prototypes
of these arms were built with a diameter of ⌀4mm and ⌀3mm. Similar instruments
with a diameter of ⌀5mm and above were published before. For the new prototypes a
rolling gear joint was developed to improve the accuracy of the arm and a gripper with
an embedded distal roll. A shape sensor prototype was developed which only needs 3
receiving fibers. The 3mm instrument was optimised with a newly developed optimisation algorithm. To combine the developed approaches, a control was implemented which
incorporates a reinforcement learning inverse kinematics and a mathematical model to
compensate for backlash and joint coupling. The 4mm instrument with 7 DOF can bend
up to 72° in each joint and has a rolling motion of 165.65°. The final 3mm instrument
has 5 DOF, including a prismatic joint, and can bend up to 82° in each joint and roll
5for 90°. The learned inverse kinematics is more precise in position and orientation error
than the common Damped least-squares Jacobian pseudo-inverse, mainly because it has
no problems with joint limits or complex situations. Using the proposed compensation
methods, the backlash was significantly reduced so that the overall average positioning
error was improved to 1.49mm.
Version
Open Access
Date Issued
2020-04
Date Awarded
2020-08
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Yang, Guang-Zhong
Thompson, Alexander
Publisher Department
Computing
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)