Model-Free Control of a Soft-Rigid Hybrid Robot for Laser-Assisted Surgery

Abstract

Soft robots possess an inherent mechanical compliance that enables safe and adaptive interaction with delicate structures and confined environments. However, their virtually infinite degrees of freedom introduce significant challenges in achieving precise and repeatable motion control. In laser-assisted surgeries, it is critical to ensure both safe tissue interaction and high precision laser targeting for effective and controlled intervention. In this work, a soft–rigid hybrid robot with onboard proprioceptive optical sensing for laser-assisted surgery is presented. The robot guides a simulated laser via fiber steering. Two model-free controllers, an adaptive Jacobian and a multi-layer perceptron (MLP), were implemented and compared for both position and speed control. Under position control, the robot tracked complex planar and spatial trajectories with an average error below 0.14 mm. Using speed control, the robot followed a circular trajectory at up to 1 mm/s with sub-millimeter accuracy. It also maintained stable behavior under unexpected external disturbances. Clinical feasibility was demonstrated by operating the robot on an in-vitro tissue phantom doped with a photochromic dye. Direct visualization of the simulated laser path on the tissue phantom demonstrated that the robot can maintain an approximately constant tip-to-target distance and spot size along the trajectory.