Model-Based Error Correction for Flexible Robotic Surgical Instruments

Robots promise to enhance minimally-invasive surgery, but flexion of the thin instrument shaft introduces error into models of the robot kinematics. Visual or electromagnetic tracking of the instrument tip provides correct forward kinematics, but uncertainty in shaft bending and port location leaves residual errors in inverse kinematics. These errors can cause incorrect motions that preclude the use of image-guidance tools. This paper proposes a model-based controller to correct the commanded motions. Comparison with a controller assuming a straight instrument shaft quantifies motion errors resulting from the use of a straight shaft controller. Analysis of the flexed shaft controller shows sensitivity to shaft length, shaft stiffness, tip force, and sensor noise.