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Tendon-driven linkage for steerable guide of flexible bending manipulation 219

mechanisms for flexible manipulation in minimally invasive intervention. The popularized
surgical robotic system, Da Vinci SP system, use fully wristed continuum instruments of
6 mm diameter to execute flexible manipulation [4]. Xu et al. developed a continuum
mechanism with serial configured flexible segments for orientation adjustment [5].
However, the continuum mechanism needs a large geometrical radius to achieve enough
bending angle. In order to reduce the bending curvature to fit a confined workspace,
concentric rigid flexible coupling mechanisms were presented in [6,7]; these structures
obtain variable bending curvature by adjusting the coupling length between the rigid and
flexible serpentine segments corresponding to the surgical task. Concentric tube
manipulator was presented in [8], which uses concentric precurved elastic tubes to form 3D
curves by changing the coupling length between the adjacent tubes. The concentric
mechanism benefit to the compact volume for achieving multiple degrees of freedom
(DOF), however it still faces the dilemma of simultaneously obtaining large bending angle
and small bending radius due to the increase in elastic impedance of the bendable segment
after increasing the coupling length between the adjacent tubes. A wire-driven multi-DOF
forceps manipulator was reported in [9]; the stainless steel ring joint with a coupling can
achieve a maximum bending angle of 45 degrees by controlling the stretch of the wires.
The bending mechanism was subjected to the large position error due to the hinge manner
of the coupling joint.

A steerable drill to create the arbitrary trajectory of a bone tunnel was reported in [10]; the
drill was mounted at the distal of the tension spring sheath with nonuniform stiffness, while
controlling the bending direction by stretching a wire along the tension spring. The
steerable drill integrated the functions of orientation adjustment and tissue drill; however
the bending radius of the tension spring is too large to execute vertical drill manipulation
inside the trachea. A transoral instrument for laryngoscope was presented in [11]; the
bending angle of the distal of the instrument can be adjusted with the assistance of the
JACO robotic arm located beside patient, which limits its dexterity in the confined tracheal
cavity. A small diameter active catheter using shape memory alloy (SMA) was presented in
[12]; it poses the advantage of small outer diameter fitting for narrow workspace. However,
the SMA actuator suffers to slow time response leading to potential risk during drill
practice.
The objective of this research is thus to understand and explore the possibilities of a
bendable surgical drill guide for MIS. The drill guide is designed to possess dexterity, with
the aim to achieve close to 90 degrees bending with a curvature of 5 10 mm at the tip
while maintaining certain rigidity and stability for the transfer of torque. The remainder of
this chapter is organized as follows: Section 9.2 describes the mechanical design of the
flexible robot. Section 9.3 evaluates the flexible robot through experiments. Section 9.4
provides the conclusions and future work.