Miniature robotic tubes with rotational tip-joints as a medical delivery platform

We present a medical-needle-sized robotic tube with multi-degrees of freedom (M-DOF) rotational hinge joints at the instrument tip, fabricated by two-axis laser micro-machining. Due to the presence of an ample working channel and direct tip controllability, this tube is a potential candidate for the precise delivery of radioactive seeds, probes and micro-forceps to regions of interest within the human body. In this paper, the advantages of the proposed hinged instrument are studied in contrast with that of flexure joints, which include-fine angle control (posability), and a shorter joint length that enables compact articulation. In addition, the joint strength both in the axial and lateral directions was experimentally investigated to demonstrate its feasibility as a robust delivery platform. Further, the intuitive nature of hinge rotation permits the use of a simple kinematic model for accurate tip motion control, under fewer simplifying assumptions than flexure joints which are impeded by material non-linearity and geometric discontinuities. An instrumented prototype was used to test this model by delivering a laser beam along a prescribed path (synonymous to simple ablation tasks). The observed RMS position error for the projected beam was \sim0.364 mm.