IEEE Robotics & Automation Magazine - June 2013 - 83

incorporate brittle sensing elements,
such as silicone-based diaphragms or
Gold/PDMS
piezoresistors, are not reliable for
Nanocomposite
robotic manipulation. Previous efforts
Tapered Fiber
have been hindered by rigid subApplied
(b)
strates, fragile sensing elements, and
Pressure
Light
complex wiring.
Output
Moreover, the polymeric solutions that can be found in literature for the fabrication of pressure
sensor systems [10]-[14] require
PDMS
complex fabrication processes and
Light
(a)
postprocessing analysis. These
(c)
Source
drawbacks can be compensated for
by using flexible optical fiber sen- Figure 1. (a) Schematic configuration of the first prototype optical pressure sensor.
sors and transducers. In addition, (b) Model of the nanocomposite material with gold nanoparticles used for the light
optical fiber sensors are immune to coupling. (c) Photo of the fabricated prototype sensor with light going out from the
tapered fiber profile.
electromagnetic (EM) fields and
can be easily multiplexed and integrated with small light emitting diode (LED) sources, effective refractive index near the coupling interface
thus providing a good alternative for the implementation (interface between the tapered fiber and GNM). The
of robotic tactile sensors [15]-[23]. Therefore, in this increase of the coupling is due to the applied pressure.
article we present a newly designed optical fiber force
sensor based on the EM coupling effect. The prototype Technological Aspects and Design
sensor is illustrated in Figure 1(a): a tapered multimode The technological aspects and the pressure application
Si fiber couples the EM field originating from a broad modalities of the proposed sensors are illustrated in detail
band-lamp source with a flexible polymer-GNM illus- in Figure 2. In particular,
trated in Figure 1(b).
Figure 2(a)-(d) refer to
A PDMS polymer film was chosen for the proposed the proposed prototype.
Sensory information from
sensor because of its ability to generate gold nanoparticles The bottom half of the
starting from gold precursors [24], [25]. Moreover, PDMS tapered fiber is embedthe human skin for feeling
presents good elastomeric properties that make it possible ded in a PDMS material
to obtain a real-time pressure sensor response. The sensor to improve its mechanimaterials and determining
illustrated in Figure 1(c) is the optimized version obtained cal stability. The PDMS
after previous preliminary studies, where the key parame- is obtained by a classical/
their physical properties
ter was the PDMS-gold controlled thickness. The half- chemical procedure (a
diameter GNM thickness is chosen for two important curing agent with a 1:10
is provided by sensors
reasons. The first reason is technological: accurate control weight ratio to base polyof GNM deposition is actually difficult, which is why we mer is used). We control
in the skin.
decide to choose the fiber diameter as a reference level. the deposition of PDMS
The second reason is an economic one: the idea was to by using the initial liquid
decrease the amount of gold quantity in the perspective of state of the PDMS; hence, we added liquid PDMS to
a possible industrial-oriented production. The first proto- immerse only half-tapered fiber, as illustrated in Figure 2.
type is based on a nonintegrated
cap of PDMS-Au material placed on
a tapered fiber [26]. For this first
A
Air
prototype, we have observed a
Pressure
Air
GNM
low sensitivity in the order of
GNM
approximately 20 g. The choice of
PDMS
PDMS
half-embedded fiber, as shown in
A'
Figure 1, is due to the possibility of
(a)
(b)
(d)
(c)
allowing an optical integrated system to provide better mechanical
stability and, finally, to perform Figure 2. Technological aspects and pressure application modality of the proposed
sensors. The tapered fiber is half embedded in PDMS and half in PDMS-Au material.
higher sensitivity. The sensitivity Longitudinal section of the prototype (a) without and (b) with applied pressure.
can be optimized by increasing the Cross section AA' of the prototype (c) before and (d) after the application of pressure.
june 2013

IEEE ROBOTICS & AUTOMATION MAGAZINE

Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - June 2013