A Two-Segment Continuum Robot With Piecewise Stiffness for Maxillary Sinus Surgery and Its Decoupling Method

With the use of tendon-driven continuum manipulators, it is possible to reach deep-seated small lesions in a constrained anatomical space. This circumvents the difficulties encountered by existing straight endoscopes and surgical instruments, which require direct line of sight access during inspection and operation. However, maintaining adequate stiffness while ensuring smoothness and flexibility during operation for a continuum robot with a small diameter is difficult. In this article, we present the design, modeling, and validation of a new two-segment continuum robot for maxillary sinus surgery. It addresses the coupling effects that can affect the safety and precise operation within the maxillary sinus. To overcome potential distal-to-proximal deviations, a piecewise stiffness structure for the continuum manipulator is proposed. Modified kinematics, based on variable curvature continuum kinematics, is used to resolve motion coupling, and a model of the continuum manipulator with varying stiffness is proposed, with due consideration of tension coupling. Experiments are carried out to validate the proposed design, modeling, and compensation schemes. Results show that the proposed manipulator can flexibly and accurately reach the target positions in the maxillary sinus model. Comparisons of continuum robots with and without the proposed compensation schemes demonstrate the practical value and potential clinical use of the proposed method.