Page 102 - Flexible Robotics in Medicine

Flexible steerable manipulator utilizing complementary configuration 87

wherein the distal-most segment of (a), which is one of the said ball bearings, is coupled to
(b); the proximal end of (a) is connected to (e) via a passive flexible tube; (b) is equipped
to an end effector which can be but is not limited to a pair of forceps; (c) is terminated on
(b) at the distal end and extends through said cylindrical segments in (a) and said passive
flexible tube before terminating at the proximal-most segment of (a); and (d) is terminated
on (b) at the distal end and extends through said cylindrical segments in (a) and said
passive flexible tube before terminating at (e).

The ball bearings have a cross-sectional diameter marginally larger than the inner diameter
of the cylindrical segments, thereby allowing the bearings to rest in the inner circumference
of the cylindrical segments, with a portion being encapsulated by the cylindrical segments.

The cylindrical segments are coupled alternately to form a series of ball joints, whereby the
cylindrical segments can pivot about said ball bearings such that they are tilted at an angle
with respect to the adjacent cylindrical segment. The cylindrical segments have eight
grooves which are spaced equally around its inner circumference and extend axially along
with the height of the cylindrical segment.

The element (c) is composed of four coupling cables extending through the grooves of the
cylindrical segments, thereby constraining and coupling said segments in (a) together. The
element (d) is composed of four driving cables extending through the grooves of the
cylindrical segments, whereby tensioning a single driving cable brings one side of all the
cylindrical segments toward each other to induce bending of (a) in one direction. The
coupling cables and driving cables are kept constrained within the grooves by the
engagement of the ball bearing on the inner circumference of the cylindrical segments.
The tensioning of the driving cables enables at least two degrees of freedom in the bending
of the distal tip of the manipulator. The prototype further includes variations in several
grooves in the cylindrical segments and variations in the number and arrangement of the
driving cables and coupling cables.

4.3 Design verification

We produced a prototype with VeroClear cylindrical segments and a distal connector via 3D
printing with Stratasys Objet260 Connex 3D printer. This was coupled with off-the-shelf
polymer beads, nylon threads as driving cables, and metal threads as coupling cables to
produce a flexible manipulator capable of achieving an average bending angle of 147 degrees
in each direction. This wide bending angle can be further improved via more precise
fabrication techniques as well as suitable materials. Moreover, increasing the number of
segments could further increase the bending angle. Our prototype will then be able to enhance
access to a greater range of areas.