Model-Based Error Correction for Instrument Flexion in Robotic Surgery

Surgical robots can improve the safety of minimally invasive surgeries through image guidance and motion filtering, but design choices that reduce patient trauma (e.g., thin instrument shafts) lead to intraoperative variation in kinematic parameters. The resulting kinematic errors can degrade image-guidance methods and cause instrument motions in undesired directions. This work addresses the most significant kinematic errors: quasi-static instrument shaft flexion and motion of the port through which the instrument is introduced into the patient. First, a metric is presented to determine the impact of kinematic errors on instrument motions. The metric quantifies how closely an erroneous robot controller will move the instrument to its desired position in a single step, as well as the worst-case angular difference between desired motions and actual motions. Simulations and experiments demonstrate results for kinematic errors due to port motion. Uses for the measure include predicting monotonic convergence, path planning, and robot design.