A Closed-Loop Controller for a Continuum Surgical Manipulator Based on a Specially Designed Wrist Marker and Stereo Tracking

Continuum structures have been widely deployed in MIS (Minimally Invasive Surgery) due to its intrinsic dexterity and compliance. However, the absolute tip positioning accuracy of a continuum manipulator may be low compared to a rigid-linked serial manipulator due to its actual bending behaviors that are often different from the assumed ideal ones. Even though the movement accuracy can be improved by motion calibration and actuation compensation, the errors caused by external loads will still exist. In order to improve the tip positioning accuracy of a continuum surgical manipulator, this paper proposes a proof-of-concept approach via integrating a specially designed wrist marker and a closed-loop controller with the visual feedback from a stereo endoscopic camera. The corner detection of the wrist marker was firstly achieved via a modified corner detection algorithm. Then, the tip position was obtained via a pose estimation algorithm that seeks position and orientation of the wrist marker when the corner points in the two images from the stereo endoscopic camera were aligned with the actual corners of the wrist marker. Experimental verification showed that the tip positioning errors were reduced to 25.23% of the original errors during trajectory tracking, demonstrating the effectiveness of the proposed approach.