Page 245 - Flexible Robotics in Medicine

234 Chapter 10
Table 10.1: Comparison of various actuation methods.

Method Advantages Disadvantages
Shape memory alloy, also High work density 1 Long actuation time 22
known as muscle Force/mass ratio 11 De-actuation depends on convective
wires [27] Direct electrically activated heat loss 22 22
force generation and Poorer efficiency, the major part of
deformation 1111 injecting energy released as heat
Quiet 1111 1 2 222
Small 1111 Stroke length percent 22
Light 1111 Slow response 222
Simple mechanical structure
1111 1
Pneumatic actuation Keep force/torque with minimal Rupture from air pressure is possible
energy consumption 11 2 2222
Precise control 1 Low portability due to the bulkiness
High power density 11 of equipment 22222
Operation is fast 1111 1 Airtight 22 222
Low heat dissipation 11 1 Air lines, pressure pumps, or
reservoir tanks needed 22 222
Electric motors [28] No air lines, pressure pumps, Large power consumption due to
or reservoir tanks needed electrical heating 2222
11 1 Complicated structure 222
Easily measurable and Bulky size 222
controlled by electronic units
1111 1
Fast response 11
Thermal actuators Producing large displacement Large power consumption due to
[29,30] (thermal 1 electrical heating 2222
bimorphs) Slow response 222 22
Piezoelectric actuators High bandwidth11 1 High voltage needed to produce
Low weight1111 significant force or displacement
Simple mechanical structure 22 2
1111 1 Normally used in conjunction with
Can produce precise and electric motors 222 22
delicate movements 11 Fragile 2 2222
Transduce sensing is possible Small strain/stroke percent
11 1 2 2222

Referring to Table 10.1, the actuation methods thought to be appropriate for this project
were shortlisted to just the SMA actuation. Based on Fig. 10.1 and Table 10.1, SMA
actuation is considered to be most appropriate for this application.

10.2 Materials and methods

10.2.1 Shape memory alloy

The SMA wires used in the fabrication of the tentacle were obtained from Dynalloy Inc.
(California, United States). The selection of SMA wires for the tentacle is carried out based on