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Introduction: The steerable laparoscopic instrument prototype DragonFlex was recently developed with the vision of a minimalistic fully functional design, readily produced by additive manufacturing and requiring little assembly. Steering functionality is provided by rolling joints that, besides simplifying the assembly, help minimise cable fatigue and equalise force requirements on steering cables. However, the perfectly circular rolling joint design introduced some mechanism play, undermining the joint's bending stiffness. Hence, the aim of this paper is to present an innovative solution for play reduction in rolling joints., Material and Methods: The original play-compensating mechanism, a shaft-embedded compression spring, proved unsatisfactory for play reduction. Therefore, a new non-circular rolling joint curvature was designed with the objective to compensate for any cable slack and thus minimise the joint play. The new rolling joint design was evaluated in several tip deflection experiments and compared to the original one., Results and Conclusions: The experimental results proved that the optimised rolling joint curvature significantly minimises play, thus being a major improvement compared to the original design. The optimised rolling joint was implemented in a new real-scale DragonFlex prototype. The presented optimisation method enables elimination of a conventionally used cable tensioning device and it is generally applicable to steerable minimally invasive instruments that use a rolling joint.

Introduction: Steerable instruments are a promising trend in minimally invasive surgery (MIS), due to their manoeuvring capabilities enabling reaching over obstacles. Despite the great number of steerable joint designs, currently available steerable tips tend to be vulnerable to external loading, thus featuring low bending stiffness. This work aims to provide empirical evidence that the bending stiffness can be considerably increased by using fully actuated joint constructions, enabling left/right and up/down tip rotations with the minimum of two degrees of freedom (DOF), rather than conventional underactuated constructions enabling these rotations with more than two DOF., Material and Methods: A steerable MIS instrument prototype with a fully actuated joint construction was compared to state-of-the-art underactuated steerable instruments in a number of tip deflection experiments. The tip deflections due to loading were measured by means of a universal testing machine in four bending scenarios: straight and bent over 20°, 40° and 60°., Results and Conclusions: The experimental results support the claim that a fully actuated joint construction exhibits a significantly larger bending stiffness than an underactuated joint construction. Furthermore, it was shown that the underactuated instrument tips show a considerable difference between their neutral positions before and after loading, which could also be greatly minimised by full actuation.