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A Loop-Shaped Flexible Mechanism for Robotic Needle Steering

The ability to steer a needle around delicate or bony structures during needle insertion for targeting tumors is promising from the viewpoint of improving the effectiveness of needle insertion. In this letter, a novel flexible mechanism called “Active Sheath” is proposed for realizing shape-controllable cannulas by using only two flexible elements. Then, a steerable needle with an outer diameter of 1.3 mm and a conical tip is presented based on the proposed mechanism. In addition, a robotic manipulator is presented to control the proposed needle precisely to the right and left by using only one translational joint. Based on numerical simulations of Active Sheath using the finite-element method, a dual parallel curve model with constant curvature is developed to describe the Active Sheath system. In the experiments, the curving response of the needle to the various inputs is assessed and the results are compared with those obtained using the kinematic model. Moreover, the shapes of the controlled needles inserted into an agar phantom are investigated and compared with those of a stainless steel bevel-tip needle and a beta-titanium flexible bevel-tip needle. The prototype steerable needle with a conical tip can bend a lateral distance of approximately 91% of that of the beta-titanium flexible bevel-tip needle in 100-mm insertion trials. The proposed flexible mechanism and the steerable needle prototype have the potential to create curved paths through shape-control commands during needle insertion.