Force and Stiffness Control of Continuum Robots for Minimally Invasive Cardiac Surgery

  • Hessa Al Falahi

Student thesis: Master's Thesis

Abstract

Considering the fertile, rapidly growing research on minimally invasive surgical manipulators, this thesis presents the first passively controlled robotic catheter for optimal, pseudo-constant contact force with the beating heart during minimally invasive cardiac ablation. Briefly, cardiac ablation is the conventional procedure for treating arrhythmia patients, of whom some accessory pathways within the heart initiates premature electrical signals that result in irregular contractions, usually faster than normal. During the procedure, such diseased areas are exposed to radiofrequency energy to be transformed into scar tissue, thereby restoring the normal heart rhythm. Despite this, the procedure is characterized by low success rate due to the intermittent contact with the moving heart tissue, that leads to inefficient energy delivery tissue and incomplete blockage of the diseased tissue. The robotic catheter designed and fabricated in this thesis is capable of achieving pseudo-constant contact force with the tissue at a prescribed force value as per the surgical requirements. The novelty of this work lies in the development of a statically-balanced compliant mechanism composed of (1) distal bi-stable concentric tubes and (2) a compliant, torsional spring mechanism that provides torque at tubes proximal extremity. The energy released by the tubes upon snapping from one stable-equilibrium position to the other is compensated by the energy stored in the torsional spring at the base, thereby resulting in the first, energyfree, zero stiffness catheter system that (1) synchronizes with the motion of the heart and (2) naturally results in optimal, pseudo-constant contact force with the tissue. The formulated mathematical model, simulation results and the physical prototype which has been experimentally tested, prove the feasibility of the robotic catheter. It is foreseen that such a catheter with a compliant, mechanically sufficient distal bandwidth is of high clinical impact. Furthermore, the developed variable stiffness mechanism at the base shows promising results as will be discussed in this these, thereby constituting the first catheter that naturally satisfies the surgical requirements in terms of tip forces, while precluding the computationally demanding control architectures in the case of active control.
Date of AwardApr 2020
Original languageAmerican English

Keywords

  • Concentric Tube Robots
  • Cardiac Ablation
  • Minimally Invasive Cardiac Surgery
  • Variable Stiffness Mechanism
  • Passive Force Control.

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