4-DOF tendon-actuated surgical wrist

Commercial robotic surgery wrists such as the da Vinci EndoWrist are closed systems priced far out of reach of the labs and hospitals that would most benefit from them. The question was whether a 4-DOF branched wrist with comparable dexterity could be built from low-cost tendon actuation and described well enough to control.

• Designed a 4-DOF tendon-actuated branched wrist inspired by the da Vinci EndoWrist, sized for low-cost manufacture and 3D printing.
• Derived closed-form forward and inverse kinematics for the branched topology, rather than solving numerically at every step.
• Analysed the reachable workspace, manipulability across it, and the jaw aperture available at each pose.
• Built a Simulink/Simscape Multibody pipeline that runs trajectory to inverse kinematics, per-DOF PID, the Simscape plant and back out through forward kinematics, so commanded and achieved poses can be compared directly.
• Wrote an interactive MATLAB GUI that renders the linkage in 3D live while the solver runs.

• Closed-form point-target inverse kinematics validated to roughly 8e-13 mm error.
• The same solution cross-checked against an independent Python replica written from the derivation rather than from the MATLAB code.

Research internship in the Mechatronics department, IIT Delhi, May 2026 to Oct 2026, supervised by Prof. Jitendra P. Khatait and Dr. Deepak Kumar. I did the design, derivation, simulation and GUI work. The thesis was delivered in October 2026.

• Validation so far is numerical and in simulation. Tendon friction, backlash and the compliance of printed parts are not in the plant model, and they are what will dominate on hardware.
• The per-DOF PID controllers are decoupled, so they ignore the tendon coupling the branched routing introduces.
• Next step is bench testing the printed wrist against the simulated trajectories, and identifying the tendon transmission from that data.

Code to be released with the paper.