Page 381 - Control Theory in Biomedical Engineering

Tunable stiffness using negative Poisson's ratio 347

Fig. 26 (A) Folding crease pattern. (B) Completed collapsible tower.

This origami structure can be collapsed into a small unit, but can also
show an excellent load-bearing ability when fully extended. This particular
structure can carry as much as 200g before starting to collapse.
The existence of variable stiffness in this structure is not only observed
visually but can also be rigorously proven using kinematic models (Zhai
et al., 2018). To verify the existence of stiffness variation, the deformation
energy of the triangulated cylinder patterns and the extension and collapsing
from the energy and strain perspectives is analyzed (Zhai et al., 2018).
A unit cell from the triangulated cylinder and the same triangle in the
folded state is shown in Fig. 27.

C
r
b
Ø
n collapsed flaps Extended flaps h
a C
A
A a B y z
B
y
x
x
Fig. 27 Unit cell parameters, folded and extended cylinder parameters (Kolken and
Zadpoor, 2017).