Page 123 - Flexible Robotics in Medicine

Modular origami joint operator to create bendable motions with multiple radii 109

Figure 5.5
Vacuum-actuated prototype top half. The vacuum pulls the latex skin down instead of pulling the
modules together.

was positioned over the notch but under the tube so that the drilling wire was outside the
bag. However, having the latex bag over the notch but under the tube caused excess
loose latex skin between the modules and resulted in the vacuum pulling the bag down
instead of drawing the modules together. Therefore the module head was not able to
bend much.
Having a notch in the module was incompatible with vacuum actuation. Thus the only
alternative was to attach the tubes onto the latex bag, but this method would not work
for bending a stiff material such as the Nitinol drilling wire because it would tear the tube
out from the bag or tear the bag itself. Furthermore, the wire could not be within the bag
since it must drill through the bag to reach the trachea, and this would create a hole,
causing the vacuum to release. However, it would be possible to use this design with
a transparent bag to bend a more flexible material such as a fiber-optic wire for
endoscopy.
5.2.1.1 Pneumatic casing

The device was actuated by negative pressure. The prototype was encased in an elastic
casing (Fig. 5.5). Voltage was used to vary the pressure generated inside the elastic casing,
making the device controllable. It was essential to ensure that there were no leaks in the
casing as leaks could result in pressure loss. As the negative pressure increases, the
prototype compresses, and the various segments bend. The device has two DOF when it is
not actuated and can therefore move about two planes. Upon actuation, it has one DOF and
moves predominantly in one plane.

5.2.2 Tendon-actuated prototypes

Since the vacuum actuation method had problems implementing the drilling function,
tendon actuation was implemented as an alternative. By pulling on the tendons, the device