Modeling Telescoping Tendon-actuated Continuum Robots

Tendon actuation is the most common method for producing flexure in continuum medical devices. Examples include catheters, ureteroscopes, bronchoscopes and colonoscopes. These devices are comprised of an elongated tube with a short steerable tip portion and a long passively flexible proximal portion. The shape of the proximal portion conforms to the shape of the body lumen as it is advanced into the body while the tendon-actuated tip portion provides for tip positioning and steering. While many of these devices are comprised of a single elongated tube, there are important clinical examples for which a single steerable tip section is insufficient and the increased steerability provided by additional telescoping steerable sections is needed (Fig. 1). For example, the delivery systems used for heart valve repair and replacement employ 2-3 tendon-actuated telescoping sections [1]. Additional examples include Hansen Medical’s robotic electrophysiology catheter [2] and Auris Health’s robotic endoscope for peripheral lung biopsies [3] each of which possess two telescoping steerable sections. While a variety of models mapping tendon actuation to robot shape have been developed, they are all limited to consideration of a single tube [4-6]. They cannot accurately predict the shape of multi-tube robots because they do not model the twisting that occurs between the tubes. The contribution of this paper is to produce a model that includes tube twisting and to illustrate it experimentally using the system of Fig. 1.