Page 49 - Flexible Robotics in Medicine

32 Chapter 2

from inconsistent folding that resulted in minute variation in the length of the individual
edges of the folds, despite the unit maintaining a relatively straight overall 3D structure.

Another observation seen in Fig. 2.7 is the downward deflection that occurs upon inflation
when comparing the bottom vertices along the centerline of the prototype. This further
showed the effect of inconsistent folding on the successful actuation of a uniform bellows
design in a straight path. As the original origami pattern was uniformly symmetrical, it was
expected to be able to actuate in a straight manner along the centerline. Fig. 2.8 shows the
same test done using art paper material, although the diameter of the prototype was slightly
different. A comparison can be made to conclude that a thicker material would be able to
achieve a more linear expansion with less deflection observed. It is useful to note that there
appears to be a more evident discrepancy if one does not take into account the diameter
differences. A wider diameter is likely to have less deflection since the precision of folds
would be less significant in affecting the actuation.

Another observation is the effective deflation and inflation between the materials. Since a
thinner material would allow for more internal volume compared to a thicker material of
the same outer diameter, actuation by pneumatics, which is based on pressure-volume
difference, would result in a more effective linear inflation and deflation of the prototype
created from the thinner material. This can be seen from the difference in ratio change
between the deflation and inflation to the resting state for the respective materials and
thickness. Another issue that could have affected the deflection and inflation could be the
difference in the size of the robot with regards to the connected tubing to the syringe.
The miniaturized diameter of the prototype made the tubing diameter more significant,
and the prototype was thus more susceptible to being affected and displaced while handling
the syringe and tubes manually. The difference in thickness of the material used while
increasing the strength of the prototype also affected the actuation power required to
achieve the same degree of actuation due to the material properties.

Figure 2.8
Actuation of 15 mm diameter art paper prototype, showing no deflection along the centerline
upon inflation.