Optimizing Continuum Robot Tendon Routing for Minimally Invasive Brain Surgery

Tendon-driven continuum robots are compliant and capable of assuming complex curves, making them ideal for minimally invasive surgery in confined spaces with obstacles. These robots can achieve an infinite family of curves, determined by both actuation and design considerations, such as the tendon routing paths of tendons along the robot. Design optimization of surgical continuum robots has been studied (see [1] for review), but the idea of variable and complex tendon routing is newer, and although it has been modeled [2], it has yet to be used to design a practical surgical device. For tendon-driven continuum robots in general, design optimization has thus far focused on multi-segment robots that use straight (i.e. parallel to the backbone) segments of different lengths, where tendons terminate at various arclengths along the robot [3], [4]. The ad- vantage of designing with nonlinearly routed tendons is the potential to enable a much more expressive family of shapes during actuation [2]. However, it has thus far been challenging to design nonlinear tendons because one is working in an infinite design space with mechanics- based models that require solving differential equations to compute robot kinematics. Toward solving this problem, this paper presents a new tendon routing parameterization for tendon-driven robots and leverages it to optimize the routings for a de- sign objective drawn from a practical neurosurgical ap- plication: choroid plexus cauterization for hydrocephalus [5]. This application was an early motivating example in the development of concentric tube robots, extended in [6], although physical size, achievable curvatures, and stiffness constraints have thus far limited practical fabrication of the robots designed in simulation. The endoscopic approach to choroid plexus cauterization requires maneuvering through tight spaces in the ven- tricles, which is challenging with traditional constant curvature endoscopes (see Fig.1). Further, even in “suc- cessful” procedures, surgeons often want to cauterize more of the choroid plexus than they can currently reach and simply settle for what they can reach. Thus, a robot with nonlinear tendon routing that can access more of the choroid plexus would be a valuable tool.