Modeling and design of a helix-cable actuated steerable instrument for minimally invasive surgery

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Minimally Invasive Surgery or MIS is a branch of surgery focused on reducing the invasiveness of surgical procedures, accomplished by minimizing the size and number of incisions. The approach inevitable leads to confinement of the operational space and restricts the movement of the used instrumentation. In this thesis, a MIS procedure called Endonasal Skull Base Surgery (ESBS) is presented to illustrate the need for maneuverable instruments. The maneuverability of an instrument can be enhanced by adding one or multiple cable-actuated steerable elements to the tip of the instrument. Currently the cables in these (multi-)steerable instruments are placed parallel to the longitudinal axis of the steerable element. This thesis proposes the use of helix cables as means of multi-steerable actuating, wherein the cables are rotated along the longitudinal axis of the steerable element. A force driven two dimensional simulation model was developed and validated in order to analyze the actuation behavior of helix cables in a steerable element. The results enabled the creation of a mechanical control method, which is integrated in a demonstrational prototype. The prototype reveals three additional functionalities to a steerable element: 1) The expansion of the shape domain of a steerable element, resulting a higher diversity of possible direction and position combinations of the tip. 2) The incorporation of a local positional stiffness of the tip. 3) The incorporation of a sampling behavior between the control handle and tip, meaning that only cable-induced shape-modes of the handle are passed on to the tip.