Page 251 - Flexible Robotics in Medicine

240 Chapter 10

custom software, and essential electronic components. The part on the left is the joystick.
The joystick used in this application can give input about the x- and y-axis to the
microcontroller when moved. The digital output pins have connected the transistors, which
handles switching on the power coming from the batteries to control the SMA wires.
The Arduino Uno microcontroller actuates the SMA wires using the transistors as switches
that control the power being delivered. The joystick used is a resistive analog joystick and
gives data centered on the x- and y-axis. The joystick pins are connected to the
microcontroller’s analog input pins. When the joystick moves, the x and y values change
accordingly. The program directs the microcontroller such that when these values exceed a
certain threshold, it passes out current from its output pins, which, in turn, opens the current
flow on the side of the transistors.

10.3 Results

10.3.1 Bending performance of the tentacle

The tentacle structure is an elastic tube with SMA wires running through the length of the
body. The SMA wires in the tentacle are actuated based on Joule heating such that when
current is passed, the temperature is raised, and the martensite fraction converts into the
austenite phase achieving the programmed configuration. All the SMA wires are initially in
U-shaped conformation, which guides the tentacle structure to be in straight conformation
since the SMA wires are in the martensite phase and are compliant and take the
configuration of the silicone elastomer in the tentacle structure. Due to the self-weight of
the silicone elastomer, the tentacle structure tends to bend in one direction, which can be
reduced by changing the length of the tentacle structure. When actuated, the SMA wires
transform into the austenite phase and guide the tentacle structure to bend in a direction
while reaching its programmed configuration. This happens due to the higher stiffness of
the austenite phase compared to the stiffness of the silicone elastomer in the tentacle
structure. When deactivated, the SMA wires transform back to the martensite phase and its
stiffness is further reduced below the silicone elastomer, which allows the tentacle structure
to return to its initial configuration. The actuation mechanism of the tentacle structure and
its resultant bending are shown schematically in Fig. 10.6A.
The tentacle structure is actuated by applying different input currents (0.5 1.5 A), and its
corresponding bending angles are determined. The current is applied for 2 seconds and then
removed for 2 seconds, as shown in Fig. 10.7B. When the tentacle is actuated with an input
current of 0.5 A for 2 seconds, the tentacle structure achieves a maximum bending angle of
8.2 degrees; when actuated with an input current of 1.0 A for 2 seconds, the tentacle
structure achieves a maximum bending angle of 22.3 degrees; when actuated with an
input current of 1.5 A for 2 seconds, the tentacle structure achieves a maximum bending