A modeling approach for continuum robotic manipulators: Effects of nonlinear internal device friction

In recent years, flexible robotic catheter systems have been developed for minimally invasive cardiac surgery. These systems commonly include a passive flexible catheter, which is biocompatible, and an active servo system which provides the actuation for the flexible catheter. To relate control actuation motion of the servo system to catheter motion, models of continuous catheters have been developed. A typical approach is to assume a kinematic model in which the catheter maintains constant curvature along its length when articulated. However, this approach cannot explain the nonlinear behavior of the catheter when the effect of internal friction is considered. In this paper we present a lumped-parameter modeling approach that allows for the inclusion of nonlinear effects, including friction. The proposed approach has been used to model a prototype catheter where internal friction is modeled using a modified Dahl friction model. To evaluate the efficacy of the modeling approach, the simulation results were compared to an experimental catheter prototype. Results show that the proposed approach significantly improves simulation accuracy as compared to the case where friction is not considered. In addition, the effects of friction on catheter performance were investigated using the developed modeling approach.