ABSTRACT
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.