1. Supervisors: Jung Kim, Hyosang Lee, Jiseung Cho (KAIST) Acknowledgements: AlI Alazmani, Peter Culmer, KAIST
Introduction & Aim
Materials & Methods Results
Discussion & Conclusions
Mechanical Engineering Summer Internships 2016
Electronic wearables are increasingly becoming a vital technology in biorobotics to
measure the dynamics of the human body for both feedback and control of robotic
systems. Rigid sensors, such as gyroscopes have been previously used in this applications,
however they can caused discomfort and pain to the user. Recently, soft sensors have been
develop to adapt to the surface of the human body and interact with tissue without
causing any damage. 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.
Parameter Testing on Soft Strain Composite Sensor
Daniel Nakhaee-Zadeh Gutierrez
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.
The operation principle of
the soft sensor, relies on
the resistance cross-paths
and the tunnelling effect
between the disposed
carbon nanotubes. The
composite material was
pre-produced and premix
to ensure a optimal
dispersion of the
nanotubes.
Figure 2. Soft sensor parts
For the parameter testing a total of
12 linear samples with 3 different
lengths (30, 60 ad 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.
The goal of this test is to study four
characteristics: hysteresis, non -
linearity, sensitivity and range and
dynamic and oscillatory response.
0
100
200
300
400
500
600
700
800
900
1000
0 5 10 15 20 25
MeanResistance(KOhm)
Width (mm)
30mm 60mm 90mm
Figure 1. Soft sensor components and applications
The soft sensor samples were tested using
a custom extensometer (Figure 4) and a
load cell attached. A set of clamps were 3D
printed to ensure sufficient grip with the
sensors and constant signal reception. The
sensors were connected to a balanced
Wheatstone Bridge to amplified the
voltage difference.
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%).
The data was obtained using a Quarc board
and processed in MatLab.
Figure 4. Custom extensometer use
for the parameter testing
Figure 5. Preliminary results of the resistance testing done to the samples
Length:
From the preliminary results, it is possible to identify a relationship between the dimensional characteristics and the
behaviour of the sensors. 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 described the performance in
real life uses.
Overall, this project has been a great introduction to the world of biorobotics and the possibilities of using soft sensors. The
technology use in this project has a lot of benefits for both monitoring patients rehabilitation, but also to control robotic
assistive devices such as prosthetics or exoskeletons. At the same time, this sensors present multiple drawbacks compare to
the conventional rigid sensors, such as high hysteresis, instability and low frequency working range.
Figure 3. Dispenser system used for
sensor fabrication