Page 474 - Flexible Robotics in Medicine

468 Chapter 20

Figure 20.9
Actuation of the spring-based SMAHV. (A) Time-resolved displacement of the SMAHV with spring
of 100 µm diameter SMA wire. (B) Time-resolved displacement of the SMAHV with spring of
150 µm diameter SMA wire.

3 seconds relaxation phase. The time-resolved displacement of the SMAHV with 375 µm
diameter SMA wire when applied with 1.5 A input current for three cycles is shown in
Fig. 20.8B. It is observed that the SMAHV reached a maximum displacement of 1 mm for
all three cycles of actuation. The SMAHV required all of the 5 seconds of the actuation phase
to reach the maximum displacement. The SMAHV returned to the initial position during the
3 seconds relaxation phase.

20.3.2.2 Shape memory alloy spring-based shape memory alloy actuated hydrogel valve

The SMA springs in the SMAHV are actuated by applying current using an external DC
supply through copper wires. An input current of 1.0 3.0 A was applied to the SMA wire in
the SMAHV, and the displacement while decreasing the area of the lumen is video-recorded
and analyzed using Tracker 5.0 (Douglas Brownr). Each cycle of the SMAHV is actuated for
a period of 8 seconds, with an actuation phase of 5 seconds and a relaxation phase of
3 seconds. Applying an input current of 1.0 2.0 A to both 100 and 150 µm wire diameter
SMA spring in the SMAHV produced a displacement of 0.1 0.4 mm, which is very low and
renders the valve unsuitable for CBI process due to its negligible change in the lumen area.
Applying an input current of 3.0 A and above to both 100 and 150 µm wire diameter SMA
spring in the SMAHV, required longer cooling time for the SMA spring and the SMAHV was
unable to return to its initial position in the 3 seconds relaxation period. Due to these
drawbacks, an input current of 2.5 A is applied to both the 100 and 150 µm wire diameter
SMA spring in the SMAHV, to determine the displacement of the SMA spring-based SMAHV.
The time-resolved displacement of the SMAHV with 100 µm wire diameter SMA spring,
when applied with 2.5 A input current for three cycles, is shown in Fig. 20.9A.Itis
observed that the SMAHV reached a maximum displacement of 0.9 mm for all three