Page 45 - Flexible Robotics in Medicine

28 Chapter 2

In order to mimic the gait of the snake, the S-shape was essential. We choose the four-unit
design rather than a less bulky two-unit design that can only achieve a C-curve. Fig. 2.4
illustrates the inflation and deflation pattern of the four-bellows units, labeled A D, to
mimic the rectilinear locomotion. An arrow pointing up indicates inflation, whereas an
arrow pointing down indicates deflation, with the adjacent letter representing the unit in
which the inflation or deflation should occur. In the figure, only full deflation and inflation
are considered as opposed to partial inflation, so the figure may not be fully representative
of the best way to achieve the desired locomotion.

2.3.3 Material selection

When the paper material was used, the robot could not be entirely flat nor fully extended
as per what rigid origami should be since the paper is not entirely rigid and inflexible,
which affects the deformation of the corners and how the vertex position is translated.
Thus the change in the angle of the folding and the volume achieved are different from the
theoretical values and require some further study, especially if the material selected varies
in thickness.
For the base material to fold the octagonal bellows units, a total of four different variations
of paper were chosen to test the difference that the thickness of the paper made to the
creasing and subsequent strength of the folded bellows. Paper was used as a template to
build the prototypes as the initial design of the prototype. Eventually, the material to be
used for further prototyping can consider other materials such as porous metal to add
sensing capabilities. The variations of paper chosen were 80 gsm copier paper, 92 gsm
tracing paper, 250 gsm art paper, and 350 gsm cardboard. The increasing thickness of the
paper across the four variations was to study the effect of thickness on the strength of the
prototype.

The range of materials used to make the different prototypes is shown in Fig. 2.5,where
there are differences in diameter as well as the thickness of the silicone-coated paper
used. Three versions (i, ii, and iii) on the left were 9 mm in diameter, where the middle
blue colored prototype (ii) used 92 gsm tracing paper, while the other two prototypes (i
and iii) used regular copier paper with the difference being the competency in folding
that resulted in an improved straighter prototype on the right. Prototypes (iv) and (v)
were further attempts where we employed increasingly thicker variations of the paper.
The white prototype (v) was with 250 gsm art paper, and the brown prototype (iv) was
with 350 gsm cardboard. Since these materials were thicker, in order to reduce
inconsistencies in precise creasing, they were etched by a penknife along the origami
creasing lines before folding into the final shape. They were also slightly bigger than
the ideal 9 mm sized prototype, as the thicker material was challenging to work with.
Pushing for smaller scaled prototypes would increase the tendency of inconsistent and