Page 428 - Flexible Robotics in Medicine

422 Chapter 19

The flexible and stable Goldrill is a drill that fulfills both design stipulations. Flexibility is
required to gain access to the tracheal lumen, and this is achieved using segmented portions
strung together by tension cables. This allows the curved organic shape of the interior of the
trachea to be navigated with ease when the tension cables are not tightened.
On the other hand, this drill also provides stability, which is much needed in the process of
drilling. The stability of this drill is achieved through the tightening of the tension wires. As
shown in Fig. 19.1, this causes the segments to link together and lock in a predetermined
curvature that is dependent on the shapes of the individual segments. This forms a relatively
stable structure that can function as a scaffolding for the drill bit, which is a flexible metal wire.
In addition to these basic design features, we have ensured that the Goldrill utilizes a
unique shape for the segment locking mechanism. This design is optimized for each point
on the device and prevents the segments from bending backward due to the bending
moment experienced when the drill bit makes contact with the tracheal wall. Thus, the
safety of patients and excellent performance in operation are ensured with a stable drill.

The general idea of Goldrill is to form a wire-controlled segmented rigid drill sheath. When
the wire is loosening, the detached segments provide enough flexibility to reach the drilling
site, and when the wire is tightening, the collapsed segments will form strictly one
stable shape, which ensures that the drill tip is perpendicular to the drill site.

The schematics of the drawing process are shown in Fig. 19.1. First, the desired parameters for
curvature are generated based on the Alberta idealized throat model (AITM). Then a cross-
sectional design that includes wire and drill bit lumen is drawn to sweep through the curvature,
creating a continuous solid body. It is also worth mentioning that AITM is not the only source
of constrictions to design. Often tracheostomy is performed when an endotracheal tube is
already inserted from mouth. Hence the inner dimension (around 18 mm) limits the bending
angle of the curvature as well as the dimension of the cross section.

For the convenience of discussion in the next sections, it is necessary to define the
nomenclature of directions (for motion) first. As depicted in Fig. 19.2, the axis used in this
report corresponds to standard anatomical ones, highlighted in different colors. Based on
our design principle, lateral and coronal movements of the tube during drilling are
improbable to happen. Hence, we will focus on the frontal/dorsal motion only.
Although we will not focus on detailed force analysis in this report, Fig. 19.3 illustrates the
force bearings during the idealized drilling motion. The lengths of arrows provide a
qualitative estimation of force strength differences. This is important for understanding the
relative interface motions.
Our device mainly consists of three parts: the bending segment, drilling needle, and
handle part.