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Title: Flexible instruments for a snake-like robot
Author: Schmitz, Andreas
ISNI:       0000 0004 9357 2816
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2020
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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.
Supervisor: Yang, Guang-Zhong ; Thompson, Alexander Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral