Page 387 - Control Theory in Biomedical Engineering

Tunable stiffness using negative Poisson's ratio 353

Fig. 36 Waterbomb tube displaying auxetic properties.

most of these applications only make use of its radial expansion characteris-
tics with little to no attention being given to its bending or twisting. By
exploring different tendon-routing mechanisms and methods of achieving
circular twist along its central axis, we were able to harness the bending char-
acteristics of the tube as well as obtain a method of variable stiffness.
Bending of this tubular structure is tricky as it relies on the careful routing
of the tendons across its complex surface structure. We tried three different
methods of routing (inner through the main channel, outer crisscross, and
outer straight; see Fig. 37), but only one structure, which involves the

Fig. 37 Various flexible bending methods of the waterbomb tube structure.