Nylon concentric tube robot

Concentric tube robots (CTRs) are made of nested, pre-curved tubes. Rotating and sliding the tubes against each other steers the tip, which makes them a good fit for reaching through narrow anatomy. At the time, this robot was intended for microlaryngeal surgery, and the project aimed to improve the robot’s overall capability.

Multiple constant-curvature nylon tubes

Sept 2021 – Apr 2023

Published as A. Lu, F. Ramos, J.-T. Lin, and T. K. Morimoto, “Enabling Higher Performance Concentric Tube Robots via Multiple Constant-Curvature Tubes,” 2023 International Symposium on Medical Robotics (ISMR), Atlanta, GA. Oral presentation.

• Modeled the robot’s kinematics with Cosserat rod theory, solved as a two-point boundary-value problem
• Simulated 50,000 sampled configurations and compared designs on four metrics: workspace volume, orientability, dexterity (Jacobian condition number) and stability
• Built what the paper describes as the first fully nylon CTR with dimensions comparable to a standard Nitinol tube set: Nylon 12 tubes with outer diameters of 1.98, 2.64 and 3.3 mm and an average clearance of 0.15 mm
• Shaped the tubes by heat-setting them in a laser-cut acrylic jig, followed by a water quench
• Validated the hardware with an NDI Aurora electromagnetic tracker over 13,000 randomly sampled joint values
• Key result: two multiple constant-curvature tubes can match a standard three-tube single constant-curvature design

Actuation system

June 2023 – June 2024

• Designed a modular actuation system for the robot, built to mount on the da Vinci Research Kit (dVRK)
• The final design uses three modules and tolerates 16× the torque of the lab’s previous actuation design
• Verified positioning accuracy with an electromagnetic tracker, comparing measured tip movement against commanded positions