Towards Force and Torque-controlled Concentric Tube Robots using Sliding-rod Modeling and Capstan Actuation

  • Taif Jasim Altaffaq

Student thesis: Master's Thesis


Due to the rapid advancement of robots and the continuous growth of their control methods, proposed design and control systems are developed. This thesis proposes a new design of Concentric Tube Robots (CTR) using the capstan mechanism for the first time in such an application. The capstan mechanism is mostly applied in haptic devices for a smooth transition of force and torque and more accurate control. It is characterized by its low backlash, its reversibility and it is well-posed to control torque and forces. The main objective of this research is to provide better forces' control at the tip position of CTR against human body tissues in Minimally Invasive Surgeries (MIS). A 3D model of the proposed CTR design was created using SolidWorks Software. A prototype is created with three Nitinol tubes linked concentrically where two of them are actuated. In addition to a compact Arduino control circuit with minimized wiring complexity. The built prototype is used for experimental validation of the new proposed Piece-wise Variable Strain (PVS) approach applied on the static setting of CTR. This novel mathematical approach of CTR control allows to use insertion forces and torque to provide better control. An analytical MATLAB simulation is created based on the PVS model. Then, a validation of this MATLAB simulation is performed, and the results are compared to the model's solution. Also, motor characterization of torque and linear motion is completed to provide better control during the experimental validation.
Date of AwardDec 2021
Original languageAmerican English


  • Continuum Robots
  • Concentric Tubes
  • Force Control
  • Capstan
  • Actuation.

Cite this