Page 94 - Flexible Robotics in Medicine

Flexible steerable manipulator utilizing complementary configuration 79

Conversely, flexible systems are defined as either serpentine or continuum [15]. Flexible systems
of the continuum nature tend to take on the form of a single continuous element, such as a
flexible tube or multiple concentric tubes. Bending relies on varying material properties, such as
stiffness or thickness in different sections or layers of these tubes, as well as their structure in
terms of incision of notches along the body of the tubes. Examples of patents that make use of
rigid and flexible systems include US8721530 B2 and US20130197306 A1, respectively.

Endoscopes, which are segmented serpentine systems, are generally less than 1.2 cm in
diameter, as they are intended for use in larger body cavities such as the gastrointestinal
tract. Most can achieve minimum bending angles of approximately 70 degrees. There is a
need for a flexible manipulator design that can be fabricated with a diameter of 3 mm or
less to be used in the narrower transluminal cavity. At the same time, it must be steerable
and actuated to achieve similar or even greater bending angles such that the area of
operation of the end effector can be increased. More importantly, this flexible, steerable
manipulator should be capable of omnidirectional bending in a stable manner.

4.2 Methods

A biopsy has conventionally involved the use of rigid forceps that are not capable of
conforming to the shapes and contours of the transluminal cavity. This limits the range of areas
from which biopsies can be obtained and creates difficulties for operators. Current endoscope
technology has limited options of EAIs that are actively controlled (i.e., the ability to control
bending curvature). Some of the current state-of-the-art flexible, steerable manipulators have
been designed specifically for use in larger body cavities such as the gastrointestinal tract. The
proposed design focuses on the distal tip to which the forceps will be connected.
Our prototype is a flexible cable-driven manipulator which has a segmented serpentine
design that can be scaled to 3 mm in diameter, suitable for use in the transluminal cavity.
Equipped with a pair of forceps as the end effector, the prototype can enhance the safety of
biopsies by reducing contact of the manipulator with the walls of the transluminal cavity
during the procedure. Moreover, the accuracy and efficacy of biopsies are enhanced, as it
enables tissue samples to be obtained from areas of interest. Bending of the flexible
manipulator and operation of the end effector are actuated by cables, which extend to a
control system and handheld prototype at the proximal end of the prototype.
The novelty of our design lies in the use of a combination of hollow cylindrical segments
with grooves and ball bearings to form the flexible body of the manipulator. This creates ball
joints that allow stable omnidirectional bending of large angles while enabling the full
prototype to be more compact by having cables extend axially through grooves instead of
holes. These segments complement one another in function and structure and can be easily
fabricated and miniaturized. This prototype presents much potential in being applied to
endoscopic diagnostic and surgical procedures, especially those conducted in confined spaces.