Model-based Parameter Selection for a Steerable Continuum Robot - Applications to Bronchoalveolar Lavage (BAL)

Bronchoalveolar lavage (BAL) is a minimally invasive procedure for diagnosing lung infections and diseases. However, navigating tortuous lung anatomy to the distal branches of the bronchoalveolar tree for adequate sampling using BAL remains challenging. Continuum robots have been used to improve the navigation of guidewires, catheters, and endoscopes and could be applied to the BAL procedure as well. One class of continuum robots is constructed from a notched tube and actuated using a tendon. Many tendon-driven notched continuum robots use uniform machining parameters to achieve approximately constant-curvature configurations, which may be unsuitable for traversing the tortuous anatomy of the lungs. This paper presents a model that predicts the curvature of a robot with arbitrary notch shapes subjected to tendon tension. The model predicted the deflection of rectangular, elliptical, and sinusoidal notches in a 0.89 mm diameter nitinol tube with 2.32%, 3.65%, and 6.32% error, respectively. Furthermore, an algorithm is developed to determine the optimal pattern of notches to achieve a desired nonuniform robot curvature. A simulated robot designed using the algorithm achieved the desired shape with a root mean square error (RMSE) of 1.52°. Additionally, we present a model for predicting the shape of nonuniformly notched continuum robots which incorporates friction and pre-curvature. This model predicted the shape of a continuum robot with nonuniform rectangular notches with an average RMSE of 5.20° with respect to the actual robot. We also demonstrated navigating the continuum robot through a pulmonary phantom.