Structurally-redesigned concentric-tube manipulators with improved stability

Concentric-tube manipulators could experience a snapping-through motion that negatively impacts their smooth operation. This may limit their adoption in the operating room, despite their advantage of enabling dexterity within a highly confined space. In this paper, we demonstrate through the kinematics of concentric-tube robots, how this adverse effect of torsion could be reduced or potentially eliminated. As proof of principle, we demonstrate experimentally and numerically that by adopting tubular composite structures, such as multi-layer helical tubes or cellular tubes, that could be designed to exhibit higher torsional-to-bending stiffness ratio, the stability margin of concentric-tube robots can be improved up to 40%. This will allow concentric-tube robots to achieve even a higher dexterity within a more confined space.