Page 244 - Flexible Robotics in Medicine

Soft-bodied flexible bending mechanism with silent shape memory alloys 233

elastomers can also be used as actuators apart from pneumatic expansion methods [14].
Elastomeric origami [15] with embedded pneumatic actuation systems [16] has also been
explored. Origami-based soft robots also demonstrated twisting (#420 degrees) modes of
actuation apart from bending modes but had a limiting factor of embracing heavier
workloads and reproducing precise motions. Origami-based printable robots [17] are also
used for precise motions. These robots can be actuated with SMA wires to reduce the size
and weight of the robot without compromising the actuation performance. Similarly,
bimorph actuators with conducting paper showed promising results [18].

The amalgamation of hard and soft materials can achieve hybrid robots to produce a
wheeled robot and a four-legged quadruped robot [19] to move over flat terrain using
electric motors and also act as a gripper using pneumatic systems. The combination of hard
and soft robots has the potential to complement and cover up the weaknesses of one another
[20,21]. In another paper, similar work was done whereby rapid prototyping was applied to
fabricate robotic structures, without requiring assembly [22]. A three-legged manipulator,
along with a four degree of freedom finger, was created using stereolithography. Actuation,
in this case, was achieved by SMA running through pivots points along the length of
fingers that are crimped near the palm area [23].
We propose an SMA-actuated elastomeric tentacle structure fabricated by soft casting. The
SMA is actuated through Joule heating, allowing the wire to bend based on the
programmed shape [24,25]. An external DC power source or battery could be used to
actuate the SMA in the tentacle. Under materials and methods, we conceptualize the mold
design, materials used in fabrication and steps involved in the assembly process, and control
methods of the tentacle. The control of input current and its corresponding deflection in the
tentacle will be explained. In the discussions section, the comparison of the current
prototype with the endoscopes available in the market is mentioned. The different actuation
modes suitable for this application are compared in Fig. 10.1 and Table 10.1.

Figure 10.1
Power/weight ratio of different actuators [26].