Page 332 - Control Theory in Biomedical Engineering

Continuum NasoXplorer manipulator with shape memory actuators 305

a larger bending angle and has the potential to reduce the diameter and to
improve end-user control. The large bending angle allows better imaging of
the nasopharyngeal region, and the soft robotic flexible tip possibly reduces
patient discomfort. These aspects of the NasoXplorer aim to encourage
more patients to conduct home-based nasopharyngoscopy.

4.1 Failure mode analysis

We conducted failure mode analysis to assess various situations in which the
NasoXplorer may fail. This allowed our team to identify components that
have a higher risk of failure and provide adjustments as well as mitigation
methods to further ensure the safety of the NasoXplorer.

4.2 Remarks on the prior comparative art

Endoscopes have been around for many years. Instruments that are assumed
to be prototypes were uncovered in the ruins of Pompeii (Olympus
museum). The first recorded attempt to use the endoscope was in 1805
by Philipp Bozzini. Since then, there have more than 1000 different designs
of endoscopic devices and more than five different designs for actuators that
involve SMAs. The first generations of endoscopes are designed with only
the flexibility of the tube in mind as well as the manipulation of the flexure of
the tube. A notable mention would be the patent filed in 1967 by Olympus
Corp (US3610231A), where the flexure of the tube is controlled via a set of
cables to maneuver the narrow paths of varying curvature in the bronchi.
From then on, there were also generations of endoscopes that are rigid.
These types of endoscopes forgo flexibility in exchange for the increased
image fidelity output via solid-state imaging devices. Due to the focus on
the device being flexible, further elaboration on these types of endoscopes
is not relevant to this review.
With the unique shape-shifting properties of SMAs, endoscopes that
incorporate these technologies were developed. There were also inventions
that allowed the torsional and rotational displacement of the tip of the
device, such as US6672338B1, that created a tendon used to guide catheters
past torturous terrain. With many actuators, a precise movement consisting
of both translational and pivotal motion was achieved with a network of
SMAs placed along the length of the device and between the coils of the
spring. The sheer amount of SMAs required has the potential to produce
a massive amount of heat, which is extremely detrimental to surrounding
tissue, especially tissue that is laden with nerve endings in a sensing organ
such as the nose.