1. Daniel Nakhaee-Zadeh Gutierrez
Supervisors: Ali Alazmani and Peter Culmer Collaboration: KAIST Biorobotics Lab
School of Mechanical
Engineering
Faculty of Engineering
A literature review was perform
about the on-going research and
available products in the market.
This created the basis for the
initial design and the inspiration
for future applications. Soft
actuators have been used before I
rehabilitation devices and on
under-water biopsy equipment.
The objective of this project was to create a soft pneumatic finger grasper capable of adapting to the geometry of
different objects. The aim with this research is to create a gripper that can replace traditional robotic grippers in
delicate environments like surgery or food processing.
Modelling soft actuators is a
highly complex process since the
behaviour of hyper elastic
materials has multiple unknowns.
The model was tested using finite
element analysis (FEA) in Abaqus.
This helps to identify the
performance and the weaknesses
of the model and materials.
The sensor consisted in two main
components: a stretchable fabric,
use to attach it to the skin surfaces
and to give structural rigidity to the
sensor; a composite material,
produced by multiwall carbon
nanotubes (MWCNT) in a polymer
matrix, this part can vary is electrical
resistivity when deform or stretch.,
making it suitable as a sensing
material.
The design of soft actuators involves
various constraints including:
material, morphology, desired
motion, actuation system. All these
variables are introduced into
preliminary sketches, as a prove of
concept. Finally, all the ideas are
implemented in a 3D CAD design
using Solid Works to create
The research has served to study the
design principles and variables
related to the development and
fabrication of polymer base soft
pneumatic actuators, including
material properties and the
morphology effects in the motion.
This project is still on going and
future testing is require to create a
final product.
the actuator and
corresponding
moulds.
Pressurised Air
Air Chamber
Constraining Layer
Interaction forces between the Walls
The method used to fabricate the
grasper was an investment or wax
casting manufacturing technique.
This method uses a wax core to
create the shape of the air chamber
inside the actuator. Then, the
silicone (Dragon Skin 20) is added to
the mould and cured at room
temperature. When the polymer is
completely cured the wax core can
be removed by melting it in an oven.
The fabricated grasper showed
great performance such as rapid
actuation and relaxation and
variable angle of bending.
However, this design had a very
thick constraining layer, that
limited the range of movements.
An optimized larger version of the
actuator was also designed for
future fabrication and testing.
The goal of this project is to perform a dimensional parameter testing to a soft stretchable sensor in development, to
characterise the affects of width and length variation on the its behaviour. The purpose of the sensor is to measure
the multi-axis angle of human joints for both rehabilitation and controlling processes.
For the parameter testing a
total of 12 linear samples with
3 different lengths (30, 60 and
90 mm) and 4 different widths
(5, 10, 15 and 20 mm) were
fabricated, using a custom
dispenser, to ensure high
accuracy. The material was
then cured and tested for
irregularities using a voltmeter.
Figure 1. Currently
available soft
grasper for
industrial use
Figure 2. 3D model of the actuator
mould
Figure 3. Meshed
part using Abaqus
Figure 4. Working principle of the soft grasper
Figure 5. Fabricated soft grasper in idle (left) and deformed shape (Right)
To obtain a broad range of results for
the application the test was divided
into two parts. A frequency range
test was perform at multiple
frequencies (0.25 Hz, 0.5 Hz, 1 Hz
and 2 Hz) at a fixed strain of 40% of
the length of the sample. The second
test consisted in a constant
frequency test at 0.25 Hz with
different elongation percentages
(10%, 20%, 30% and 40).
Syringe containing
the composite
material
three-direction
moving bed
Stretchable fabric
Pressurized air
Linear Stage
Sample
3D printed clamp
Load Cell
Figure 7. Dispenser system used for
sensor fabrication
Figure 1. Soft sensor components and
applications
For this project there are four
characteristics that we are interested
in studying: hysteresis, non -linearity,
sensitivity and range and dynamic
response. This parameters can be
measured using a custom
extensometer, which records the
force, the elongation percentage,
frequency of oscillation and
resistance change in the sample. All
these data can then be process and
the sensor can be calibrated
accordingly
From the preliminary results and as
the theory predicts, larger sensors
will show lower resistivity, since
statistically there are more cross-
path of carbon nanotubes to allow
the current of electrons. However,
these results only take into account
the static response of the samples.
Future work will focused on
analysing the dynamic loading
results and describe the
performance in real life uses.
.
Thanks to this research I got the
opportunity to travel to Korea and
to experience its culture. During my
time in the country I met a lot of
……….. inspiring people, who
were also passionate
about engineering.
Moreover, I travelled to
the different regions in
Korea to learn their
history and tradition.
Figure 8. Custom extensometer used
for testing the sensors
Figure 9. Members of the KAIST
Biorobotics Lab