Model Validation and Simulation Studies : Effects of Nonlinear Internal Device Friction on Continuum Robotic Manipulators

Recently, robotic surgery systems using passive flexible catheters have been developed for minimally invasive surgical applications. The soft, atraumatic construction of these devices help reduce injury to delicate anatomical structures while providing a means of tool placement and control. To provide kinematic and control relationships, various models of continuous catheters have been developed. However, these approaches cannot explain the nonlinear behavior of the catheter when the effect of internal friction is considered. In this paper we use a lumped-parameter modeling approach developed by the authors, which allows for the inclusion of nonlinear effects, including friction. To evaluate the validity of the model, the curvature of the proposed model was compared with that of the experimental catheter at multiple articulation angles. The experimental results show good agreement between model and experiment and, importantly, help explain the variation in curvature observed in real-world devices. In addition, the validated model is used to study the effect of internal friction on a set of complex catheter motions. The simulation results showed that the tip trajectories of the model with friction had considerable fluctuation and deviation from the desired paths. According to the simulation results, the similar fluctuation and deviation from the desired paths can be expected for an actual catheter with considerable wire friction.