Method for minimising rolling joint play in the steerable laparoscopic instrument prototype DragonFlex

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.

Key words:

• Minimally invasive surgery
• steerable instruments
• additive manufacturing
• joint play
• optimisation

Acknowledgements

This research was performed within the framework of CTMM, the Center for Translational Molecular Medicine, project MUSIS (grant 03O-202). The authors would like to thank the Dutch Organisation for Applied Scientific Research (TNO) for their collaboration. Many thanks to David Jager and Menno Lageweg from TU Delft’s fine mechanical workshop DEMO for their support.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.