Page 93 - Flexible Robotics in Medicine

78 Chapter 4

biopsies [11,12]. Flexible forceps and biopsy snares can be inserted into the lumen, allowing the
operator to perform simple tissue biopsies. These EAIs are passively controlled instruments,
which means that they are unable to bend by themselves despite being made of flexible
material [6,13]. They will bend as they are inserted into the endoscope via the proximal end but
will straighten out as they exit the distal end as no forces are applied to cause their bending.
Current biopsy forceps EAIs are only able to open and close. Therefore there is a clinical
need for forceps to be actively controlled so that they can be pushed further out of the distal
end of the lumen and (a) bend to reach corners that are difficult to reach from a linear
trajectory and (b) provide more working room for the operator. This would allow the
operator to insert the EAI further out of the distal lumen to grab a target sample without
having to keep a linear trajectory. It would also improve the versatility of the biopsy
procedure and potentially shorten the time required to obtain a biopsy.
A flexible, steerable manipulator can be used within or without the working channel of an
endoscope to overcome the abovementioned problem. The distal end of the manipulator can be
steered to navigate the contours in the transluminal cavity more effectively, thus minimizing
injuries to the patient and enhancing the safety of the procedure.
Existing state-of-the-art steerable endoscopes and endoscopic manipulators are extensive and
varied in design [11 14]. The bending of the flexible portion in these designs can be actuated
using various mechanisms. The more commonly used actuation mechanisms are pressure-driven
[14], shape memory alloy (SMA) [6,15], precurved concentric tubing [7,16], and cable-driven [5].

Pressure-driven systems, such as in US Patent US6162171 A, are complex and difficult to scale
down in terms of size, as they tend to require additional channels or components to make use
of hydraulic or pneumatic pressure. The use of SMA in some designs, for instance, US Patent
US4884557, poses difficulties in controlling the precision and magnitude of bending. It is also
more complicated, as heating elements must be incorporated. Designs that make use of
precurved concentric tubing (Patent US20100057077 A1) have limited curvature variations.
Cable-driven flexible [5,8,15], steerable manipulators generally take two fundamental forms:
rigid or flexible. Rigid systems consist of multiple segments that are coupled together by
hinges or joints to form a serpentine structure. Individual unconstrained segments have six
degrees of freedom, with translation along and rotation about the three axes. Using constraint
(s), these degrees of freedom are constricted to allow for tension control and directed bending
of the manipulator. Existing state-of-the-art devices vary in the design of each segment, the
arrangement of cables, and the constraints to enhance the flexibility and stability of the
manipulator. In cable-driven manipulators, cables extend along the body of the flexible
portion of the manipulator. When a cable is tensioned, it induces bending in the body of the
flexible manipulator. Separate cables can be tensioned to selectively bend the entire flexible
body or specific regions of the body in certain directions. Moreover, these cables typically
work in pairs to form an antagonistic bending mechanism.