Cryptex Programmable Memory Mechanism (CPMM)

Abstract

In the history of medicine and surgery, a slow transition is made from open surgery to minimally invasive surgery. Nowadays, natural orifice transluminal endoscopic surgery (NOTES) is investigated and tested. A NOTES procedure includes flexible instruments, which are inserted through natural orifices such as the mouth, nose, anus or vagina. The instrument then passes transluminally towards the areas of interest. Benefits of this surgery method compared to conventional open surgery include, among others: the reduction in tissue trauma, no external scar tissue, less blood loss and a shorter recovery period. However, the method requires highly advanced medical devices that are slender and able to bend and form different paths to reach the area of interest. Bio-inspired by the movement and the propulsion of a snake, new instruments are being developed that provide a follow-the-leader motion (FTL-motion). In a follow-the-leader mechanism, the user steers the tip of the instrument. The position given to the tip is stored and passed on proximally from segment to segment. This thesis aims to improve the existing mechanically controlled FTL-mechanisms, in which the shaft is controlled with four-cable control. In this research, a cylindrical mechanical path-planning module is designed and manufactured: the Cryptex Programmable Memory Mechanism (CPMM). The cylindrical shape improves cable-control, as it can simultaneously steer one cable and its antagonist, and control the motion of a compliant shaft in one plane. Two prototypes were developed: a machined prototype and a 3D printed prototype. Both designs were manually tested in four phases: individual components and subassemblies; the key component solely; integrated design excluding the key component; completely integrated design. It is concluded that the design of the 3D printed prototype is limited by the accuracy of the parts and the material properties. The machined prototype shows promising results, as it can form diagonal and curved paths as an output. Even though the performance of the CPMM prototype leaves room for improvement, it validates that the proposed concept can provide the follow-the-leader motion.