Page 42 - Flexible Robotics in Medicine

Prototyping soft origami quad-bellows robots from single-bellows characterization 25

the snake undergo this process, the contraction wave will travel posteriorly such that the
snake can slowly move forward in a rectilinear manner [24].

2.3.1.2 Snake’s concertina locomotion
Snakes usually use concertina locomotion in tunnels, especially ones with smooth surfaces,
in which the snake’s movements that usually rely on large areas of friction are not suitable.
This type of locomotion requires a snake to keep bending and straightening its body, as it
anchors part of its body while pulling the rest of its body in the direction of motion so that
it can “climb” and progress forward. The reason for the multiple tight bending loops is to
increase anchor points to achieve enough friction to brace itself before it can push forward
to straighten to the next anchor point. In tunnels that are inclined, snakes can change the
orientation of their scales to increase anchorage by digging into the surface to prevent
slipping due to gravity [25].

Snakes often use rectilinear, and concertina locomotion, either combined or separately,
to climb surfaces, and both types of movement are similar in their ability to move
through narrow spaces. Thus both types of movement are beneficial and relevant to
biomedical applications such as colonoscopy. Concertina motion is beneficial for curved
trajectory advancement, and rectilinear locomotion is applicable for an end-effector
advancement as well as providing an alternative to the techniques such as jiggling to
prevent entanglement. However, a point to note is that a certain amount of friction is
necessary to enable the snake to be able to utilize these movements to move forward or
through tunnels.

2.3.2 Bellows design

In the process of deciding what type of origami folding would be best for this project, the
Miura or Kresling fold [26], bistable origami were considered with slight modifications, but
the simple octagonal bellows design has its simplicity and applicability.

2.3.2.1 Origami pattern

The current prototype robot design is composed of multiple identical units based on the
simple octagonal bellows origami pattern shown in Fig. 2.1. The full origami layout seen on
the left of Fig. 2.1 shows how the flat material was creased into the appropriate alternating
mountain and valley folds. The creased material was then folded to form the 3D bellows
structure displayed on the right of Fig. 2.1. Fig. 2.2 shows a close-up look at the hexagon
pattern used to fold the octagonal bellows structure. The protruding three squares on the top
and bottom of the origami layout in the left of Fig. 2.1 are necessary to close the gap that
arises from only folding duplicates of the basic origami pattern so that the folded 3D
structure is ready to be glued and coated with silicone for use.