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\begin_body

\begin_layout Title
Toward the sense of touch in snake modular robots for search and rescue
 operations
\end_layout

\begin_layout Author
Juan Gonzalez-Gomez
\begin_inset Formula $^{1}$
\end_inset

, Javier Gonzalez-Quijano
\begin_inset Formula $^{1}$
\end_inset

, Houxiang Zhang
\begin_inset Formula $^{2}$
\end_inset

, Mohamed Abderrahim
\begin_inset Formula $^{1}$
\end_inset


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\begin_inset Formula $^{1}$
\end_inset

Robotics Lab.
 Universidad Carlos III de Madrid, Spain
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\begin_inset Formula $^{2}$
\end_inset

TAMS, Department of Informatics, University of Hamburg, Germany
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{juan.gonzalez.gomez, javier.gonzalez-quijano, Mohamed.Abderrahim}@uc3m.es, 
\begin_inset Newline newline
\end_inset

hzhang@informatik.uni-hamburg.de
\end_layout

\begin_layout Abstract
Snakes modular robots are good candidates for being used in Urban Search
 And Rescue (USAR) operations because of their flexibility, good adaptation
 to the terrain and small section.
 We propose to design and build snake robots that combine three capabilities:
 locomotion, climbing and grasping.
 The last one allows the robot to remove objects for clearing the path to
 the trapped people.
 The sense of touch is key to achieving these three capabilities.
 To implement it, our novel approach is based on the idea of touch rings
 and touch strips.
 In this paper some preliminary ideas are presented.
\end_layout

\begin_layout Abstract

\end_layout

\begin_layout Section
Introduction
\end_layout

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Typical urban scenario after an earthquake.
 A highly unstructured and chaotic environment with a lot of pieces of rumble.
 Likely, there are people inside that should be rescued immediately.
 City of Puerto Principe, Haiti.
 Photo courtesy of tumundovirutal.wordpress.com 
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name "fig:earthquake-scenario"

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\begin_layout Standard
Unfortunately disasters caused by earthquakes, floods, tsunamis or hurricanes
 are very often in the news.
 In these scenarios the priority is to find survivals quickly, otherwise
 they will die.
 In urban disasters the environment is extremely unstructured, chaotic and
 full of pieces of rubble everywhere (fig.
 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:earthquake-scenario"

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).
 This makes very difficult and dangerous for the USAR (Urban Search And
 Rescue) teams to move and locate people.
 Besides, it is clear that if a building has collapsed, there will be likely
 people inside that should be rescued as soon as possible.
\end_layout

\begin_layout Standard
During the last decade, researchers around the world have been facing the
 problem of designing tele-operated robots capable of moving in such environment
s and to assist the USAR teams.
 Properties such as versatility, adaptability and flexibility are taken
 into account when designing these robots.
\end_layout

\begin_layout Standard
Yim et al.
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LatexCommand cite
key "Yim2000"

\end_inset

 were the first to propose modular robots for this purpose, due to their
 three promises of versatility, robustness and low cost.
 Miller
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LatexCommand cite
key "Miller02-snake"

\end_inset

 suggested snakes robots (consisting of yaw modules with passive wheels)
 as good candidates for moving in unstructured terrains, in a similar manner
 than real snakes do.
 Wolf et al.
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LatexCommand cite
key "Wolf03_hyper-redundant"

\end_inset

 from the Department of Mechanics at CMU developed a new concept consisting
 of an elephant trunk-like robot mounted on a mobile base.
 A camera located at the end of the trunk was used for inspecting unreachable
 areas such as small cracks and pipes.
\end_layout

\begin_layout Standard
The Japanese government is specially interested in USAR applications.
 They are funding and promoting research for the development of practical
 search-and-rescue robots.
 Prof.
 Hirose and their colleagues at the Tokyo Institute of Technology have been
 working on these robots for many years 
\begin_inset CommandInset citation
LatexCommand cite
key "Hirose04-strings"

\end_inset

.
 They have developed robots with tracks and wheels, such as Souryu, Genbu,
 Kohga, Gunryu and the latest Helios VIII
\begin_inset CommandInset citation
LatexCommand cite
key "MicheleGuarnieri2008"

\end_inset

.
 They have also proposed the snake robots as candidates for USAR applications
 because of their advanced motion capabilities: their bodies can act as
 
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legs
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, 
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arms
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 or 
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fingers
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 depending on the situation.
 Since mid 70's they have been working on the ACM snake-like robot family
\begin_inset CommandInset citation
LatexCommand cite
key "HIROSE2009"

\end_inset

.
 The ACM-R3 and R4 have passive wheels larger than the profile of the link
 that fully cover the whole body.
 This enables the snake to slide smoothly among the rubble.
 
\end_layout

\begin_layout Standard
In the Institute of Robotics at Beihang University, Zhang et al.
 have developed the JL-I robot
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LatexCommand cite
key "Zhang06-JLI"

\end_inset

.
 It is composed of three identical autonomous modules with 3 DOF joints.
 It can climb obstacles, stairs and recover itself in case of turning over.
 
\end_layout

\begin_layout Standard
One of the latest USAR robots is Amoeba-I
\begin_inset CommandInset citation
LatexCommand cite
key "LiB.;MaS.;LiuJ.;WangM.;LiuT.;Wang2009"

\end_inset

 developed at the Shenyang Institute of Automation in China.
 It is composed of three tracked modules and has nine locomotion configurations.
 It can change its configuration automatically to adapt to the environment.
\end_layout

\begin_layout Standard
Modular robots with a 1D topology can be divided into two groups: serpentine
 and snake robots.
 The former use active tracks or wheels for self-propulsion while the latter
 use body motions in a similar manner than their biological counterparts.
 A very successful serpentine robot is Omnithread developed by Granosik,
 Hansen and Borenstein at the Mobile Robotics Laboratory in the University
 of Michigan.
 It is a novel design consisting of 5 segments with moving tracks on all
 their four sides to assure propulsion even when the vehicle rolls over.
 The latest prototype is OT-4
\begin_inset CommandInset citation
LatexCommand cite
key "Borenstein2007"

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.
 Rimassa et al.
 
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LatexCommand cite
key "Rimassa2009"

\end_inset

 have developed a serpentine robot with climbing abilities.
\end_layout

\begin_layout Standard
Even though serpentine robots are very promising for USAR applications,
 they lack the flexibility of real snakes and it is difficult to attach
 to them artificial skins because of their wheels or tracks.
 Snake robots, on the contrary, are similar to real snakes and inherit some
 of their properties.
 Perambulator
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LatexCommand cite
key "Ye2007"

\end_inset

, developed by Ye et al.
 at the Shenyang Institute of Automation in China, is able to perform a
 powerful propulsion and a high mobility.
 Every segment contains a kind of omni-directional wheel with free rollers
 that enables this robot to perform the serpentine locomotion (like real
 snakes).
 
\end_layout

\begin_layout Standard
Another modular robot with high locomotion capabilities is Hypercube
\begin_inset CommandInset citation
LatexCommand cite
key "Gonzalez-Gomez2006"

\end_inset

, developed in our group.
 It can perform at least 5 different gaits: moving in a straight line (forward
 and backward), moving in a circular path, side-winding, rotating and rolling.
\end_layout

\begin_layout Standard
Our goal is to develop a new snake modular robot for search and rescue applicati
ons.
 In this paper we propose a preliminary novel design of its tactile system
 that will be used for improving the robot locomotion as well as its climbing
 and graping capabilities.
\end_layout

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Tell the organization of the paper.
 
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This paper is organized as follows...
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\end_layout

\begin_layout Section
Snake modular robots for search and rescue operations
\end_layout

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\begin_inset Graphics
	filename figures/scenario-I.eps
	scale 50

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\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
A general scenario where there is a trapped person and the access is blocked
 by pieces of rumble
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name "fig:Scenario-I"

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.
\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
Modular snake robots have a lot of potential for search and rescue operations.
 Consider the scenario shown in figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:earthquake-scenario"

\end_inset

 where there is a collapsed building (image of Puerto Principe, in Haiti).
 A USAR robot would be very helpful to explore inside the house and searching
 for people.
 The are two possible alternatives.
 On one hand, the robot can go through the bars of the window if its size
 is small enough.
 On the other hand, it can climb the wall and enter through the upper hole,
 but the robot should be flexible and have climbing capabilities.
 Snake robots could meet these requirements.
 
\end_layout

\begin_layout Standard
Now let's consider a general scenario as the one shown in figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Scenario-I"

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 where there is a person trapped inside a house.
 First (fig.
 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Scenario-I"

\end_inset

-1) the snake robot approaches the zone.
 Obviously, locomotion capabilities are needed.
 Second (fig.
 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Scenario-I"

\end_inset

-2), the snake arrives to a wall and has to climb it.
 Therefore, climbing capabilities are necessary.
 Third (fig.
 
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LatexCommand ref
reference "fig:Scenario-I"

\end_inset

-3), there are some pieces of rubble blocking the access to the person.
 The snake clears the path by grasping the objects and getting rid of them.
 Grasping capabilities are required.
 Finally (fig.
 
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LatexCommand ref
reference "fig:Scenario-I"

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-4), the robot reaches the person.
 
\end_layout

\begin_layout Standard
This scenario suggests that the robot should have at least locomotion, climbing
 and grasping capabilities.
 In previous work, our group has researched on these three areas.
 The locomotion of snake modular robots of any length has been widely studied
 and implemented on real robots
\begin_inset CommandInset citation
LatexCommand cite
key "JuanGonzalez-Gomez2008"

\end_inset

 using sinusoidal oscillators that can be programmed with low cost 8-bit
 micro-controllers.
 A novel inspired modular climbing caterpillar that combines climbing techniques
 with locomotion capabilities was designed and tested in 
\begin_inset CommandInset citation
LatexCommand cite
key "Zhang2009"

\end_inset

.
 For climbing, a low-frequency vibrating passive attachment principle was
 successfully developed.
 Moreover, grasping capabilities are being studied and simulated
\begin_inset CommandInset citation
LatexCommand cite
key "Salvietti2009"

\end_inset

.
\end_layout

\begin_layout Standard
The sense of touch is key to achieve these three capabilities.
 For locomotion, touch sensors provide the necessary feedback for enabling
 the robot to adapt its body to the terrain and therefore moving more efficientl
y.
 In addition, situations in which the robot get caught on the ground can
 be detected.
 For climbing, the attaching forces can be measured to guarantee that the
 robot will not fall down.
 Finally, the sense of touch in grasping allows the robot to apply the necessary
 force to remove objects from the path as well as optionally detecting the
 shape of these objects.
\end_layout

\begin_layout Section
Sense of touch
\end_layout

\begin_layout Subsection
Introduction
\end_layout

\begin_layout Standard
Perceiving the environment in animals needs multimodal sensing capabilities.
 Humans combine sensory information from different sources as touch, vision,
 and hearing.
 If not using any of them, there is a gap in knowledge that makes differences
 between what is sensed and what is perceived
\begin_inset CommandInset citation
LatexCommand cite
key "Kandel2000"

\end_inset

.
 Simple experiments of exploring objects after putting hands on an ice block
 for a while, therefore anesthetizing the skin, shows the difficulty of
 achieving stable grasp
\begin_inset CommandInset citation
LatexCommand cite
key "Westling1984"

\end_inset

.
 This occurs even when participants can see what they were doing.
\end_layout

\begin_layout Standard
There are several technologies and transduction principles that have been
 traditionally employed for the development of tactile sensing for robots,
 such as resistive, force, magnetic, optical, piezoelectric and capacitive
 based sensors
\begin_inset CommandInset citation
LatexCommand cite
key "Puangmali2008"

\end_inset

.
 Among them, capacitive sensors are commonly used in robotics applications.
 Despite their two major drawbacks, stray capacity and severe hysteresis,
 they are very small and sensitive.
 In addition they can be easily arranged in dense arrays.
 As an example of their high degree of integration, Gray et al.
 developed in 1996 an 8x8 capacitive tactile sensing array with 1 mm
\begin_inset Formula $^{2}$
\end_inset

 area and spatial resolution at least 10 times better than the human limit
 of 1 mm.
 Schmidt et at.
 
\begin_inset CommandInset citation
LatexCommand cite
key "Schmidt2006"

\end_inset

 designed a novel array of capacitive sensors for grasping purposes, which
 couple to the object by means of little brushes of fiber.
 Maggliali et at.
\begin_inset CommandInset citation
LatexCommand cite
key "Maggiali2008"

\end_inset

 proposed the novel idea of using a mesh of triangles for covering three-dimensi
onal surfaces.
 They have designed a triangle module witch contains 16 capacitive sensors
 and all the electronics.
\end_layout

\begin_layout Standard
Currently, it can be found commercially capacitive based touch array sensors
 such as the ones provided by ‘RoboTouch’ and ‘DigiTacts’ 
\begin_inset Foot
status open

\begin_layout Plain Layout
http://www.pressureprofile.com
\end_layout

\end_inset

.
 Also, there exists various commercial ‘capacitance to digital converter’
 chips such as the AD7147 'Captouch' chip from Analog Devices.
 It have been successfully employed for the triangle module implementation
\begin_inset CommandInset citation
LatexCommand cite
key "Maggiali2008"

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.
\end_layout

\begin_layout Subsection
Touch rings
\end_layout

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wide false
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	filename figures/touch-rings.eps
	scale 47.5

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\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
The touch rings approach for the implementation of the sense of touch in
 snake robots
\begin_inset CommandInset label
LatexCommand label
name "fig:Touch-rings"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
Real snakes have a continuous skin, like the mammals, in which the sense
 of touch is distributed uniformly throughout the whole body.
 Designing an artificial skin similar to that of the snakes, with the same
 flexibility and equipped with touch sensors, is a big challenge.
 It still has not been realized, to the best of our knowledge.
 In our approach, we propose the idea of touch rings (figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Touch-rings"

\end_inset

) located at fixed positions along the body axis.
 Therefore, the sense of touch is not continuous and uniformly distributed
 but discrete and concentrated in touch zones.
 Although it is not continuous, the distance between two consecutive rings
 (
\begin_inset Formula $d$
\end_inset

) can be set according to the application.
 If higher touch resolution is required, this distance can be reduced.
 Thus, this approach is very versatile giving the designer the possibility
 of changing it.
\end_layout

\begin_layout Standard
In our opinion, USAR operations do not require a very high resolution.
 It should be high enough to allow the robot to perform the locomotion,
 climbing and grasping efficiently.
 As a starting point we are planning to use one touch ring per module.
\end_layout

\begin_layout Subsection
Touch strips
\end_layout

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\align center
\begin_inset Graphics
	filename figures/touch-strip.eps
	scale 65

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\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
The capacitive touch strips used for implementing the touch rings
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name "fig:Touch-strips"

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\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
Each touch ring consist of a flexible capacitive strip that is bended (figure
 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Touch-strips"

\end_inset

).
 One advantage of this design is that it can be fitted into different snakes
 with different sections of the body trunk, due to the fact that the strip
 is flexible.
 In the example of figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Touch-rings"

\end_inset

 the section is circular, but it can also be applied to snakes with other
 section shape, like a square.
 The strip will fit regardless of the shape of the body section.
\end_layout

\begin_layout Standard
Therefore, our design is very versatile and it is valid for a lot of different
 snakes.
 Moreover, the width and length of the strip can also be changed according
 the application.
 The wider it is, the more capacitive sensors can be embedded.
\end_layout

\begin_layout Subsection
Capacitive sensor principle
\end_layout

\begin_layout Standard
The touch strips are based on capacitive sensors.
 The strip is composed of three layers (figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Touch-strips"

\end_inset

).
 The total thickness is expected to be less than 1mm.
 The first layer is a flexible printed circuit board (PCB) containing the
 electrodes for the capacitors.
 The second layer is the dielectric.
 This material should be compressible and expandable.
 We are testing different candidates, such as silicone (S60) and polyester
 (PEPT) based ones.
 The third layer is the ground plane.
\end_layout

\begin_layout Standard
When normal forces are applied to the strip surface, the dielectric layer
 is compressed and the distance between the electrodes and the ground plates
 is reduced.
 Therefore there is a change in the capacitance of the capacitors that can
 be measured.
 The material in the second layer must recover its initial thickness when
 no forces are applied.
 
\end_layout

\begin_layout Subsection
Electronics
\end_layout

\begin_layout Standard
Various commercial capacitive-to-digital converters chips are available.
 In this work, we are using the MPR121 from Freescale
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status collapsed

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http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MPR121
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\end_inset

 because of its low cost and I
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C bus compatibility.
 Its main features are summed up in table 
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reference "tab:MPR121-chip"

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.
 It can measure capacitance ranging from 10 pF to 2000 pF.
 Minimum size of the electrodes should be less than 0.25 cm, if high dielectric
 materials are used.
 Once capacitance is calculated, it runs through a couple of levels of digital
 filtering allowing for good noise immunity in different environments without
 sacrificing response time or power consumption.
 
\end_layout

\begin_layout Standard
Some of the major advantages comparing with the AD7147 chip include an increased
 electrode count, a hardware configurable I2C address, an expanded filtering
 system, and completely independent electrodes with auto-configuration built
 in.
 Regardless every chip can read only 12 capacitive sensors, bigger arrays
 can be made by connecting different MPR121 chips through I
\begin_inset Formula $^{2}$
\end_inset

C bus.
 When bandwidth is not enough for transmitting all chip readings, digital
 multiplexers for communications or other microcontrollers should be used.
\end_layout

\begin_layout Standard
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\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Features of the MPR121 chip
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name "tab:MPR121-chip"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout
\align center
\begin_inset Tabular
<lyxtabular version="3" rows="6" columns="2">
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Feature
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Value
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<row>
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\begin_inset Text

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Number of electrodes
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<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text

\begin_layout Plain Layout
12 electrodes
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<row>
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Measurement range
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10 pF to 2000 pF
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Sensitivity range
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-0.01953 to -0.19531 pF / ADC count
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I2c bandwidth
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\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text

\begin_layout Plain Layout
400 Khz
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<row>
<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">
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Size
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\begin_layout Plain Layout
3x3x0.6 mm
\begin_inset Formula $^{3}$
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\end_layout

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\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Section
Mechanics
\end_layout

\begin_layout Subsection
Modules
\end_layout

\begin_layout Standard
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wide false
sideways false
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\align center
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	filename figures/family-y1-cube-m.eps
	scale 58

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\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
The Y1 and Cube-M families of modules
\begin_inset CommandInset label
LatexCommand label
name "fig:Y1-Cube-M-families"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
Since 2004 our groups have been working on modular robots.
 We have designed different modules, grouped into two families: Y1 and Cube-M
 (figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Y1-Cube-M-families"

\end_inset

).
 The Y1 family is very cheap and very easy to build.
 It is intended for fast-prototyping, testings and educational purposes.
 The modules have one DOF actuated by a low-end RC servo (futaba 3003).
 The electronics (not shown in the figure) includes an 8-bit PIC16F876A
 microcontroller.
 This family is composed of three modules: Y1, RepY1 and MY1.
 The Y1 consist of 6 laser-cut pieces of plastic glued together.
 It is mainly intended for educational purposes as it is very cheap and
 easy to build by students.
 RepY1 modules are the 
\begin_inset Quotes eld
\end_inset

printable
\begin_inset Quotes erd
\end_inset

 version that can be manufactured using a commercial 3D printer or a low-cost
 open Reprap machine
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status open

\begin_layout Plain Layout
http://reprap.org/wiki/Main_Page
\end_layout

\end_inset

.
 The MY1 version is made of aluminum.
 It has three pieces that are joined together using screws and nuts.
 
\end_layout

\begin_layout Standard
The Cube-M family
\begin_inset CommandInset citation
LatexCommand cite
key "Zhang2009a"

\end_inset

 is an improvement over Y1.
 These modules are made of aluminum and are designed to carry more weight
 and to build bigger modular robots with 1D and 2D topologies.
 The electronics has been improved and embedded into the modules.
\end_layout

\begin_layout Subsection
Robot prototypes
\end_layout

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\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename figures/snakes-prototypes.eps
	lyxscale 80
	scale 51

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Some of the modular robot prototypes.
 a) Dr.
 Zhang and Dr.
 Gonzalez-Gomez sitting by their modular robots b) Hypercube snake, composed
 of 8 pitch-yaw Y1 modules.
 c) Cube Revolutions: a caterpillar with 8 pitch Y1 modules.
 d) A 2D topology star robot.
 e) A 5 pitch-yaw Cube-M module snake.
 f) A four MY-1 module pitch caterpillar going through a tube
\begin_inset CommandInset label
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name "fig:snake-modular-robots"

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.
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
Some of the modular robots we have built are shown in figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:snake-modular-robots"

\end_inset

.
 We have mainly concentrated on studying the locomotion of modular robots
 with 1D topology.
 This group can be divided into two subgroups: pitch-pitch and pitch-yaw
 connecting modular robots.
 The former is composed of those robots in which all the modules pitch up
 and down (fig.
 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:snake-modular-robots"

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c and 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:snake-modular-robots"

\end_inset

f).
 This configuration is kinematically similar to that of the caterpillars
 in nature.
 Therefore, these robots are very useful for studying the climbing capabilities,
 even though they only can move forward and backward.
 The later comprises the robots with pitch and yaw modules.
 These snakes can move on a plane (fig.
 
\begin_inset CommandInset ref
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reference "fig:snake-modular-robots"

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b and 
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reference "fig:snake-modular-robots"

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e).
 When sinusoidal oscillators are used for their control, they can perform
 at least five different locomotion gaits
\begin_inset CommandInset citation
LatexCommand cite
key "JuanGonzalez-Gomez2008"

\end_inset

: moving in a straight line, circular path, side-winding, rotating and rolling.
 The relationships between the oscillator's parameters (amplitudes and phase
 differences) determine the type of movement that will be executed.
\end_layout

\begin_layout Standard
Modular robots with a 2D topology have also been developed (fig
\begin_inset CommandInset ref
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reference "fig:snake-modular-robots"

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d) but their use for search and rescue operations is left for future work.
\end_layout

\begin_layout Subsection
Touch strip prototype
\end_layout

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	filename figures/touch-strip-prototypes.eps
	lyxscale 50
	scale 98

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\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Preliminary touch strip prototype.
 Only one layer is being tested.
 a) The touch strip with 12 electrodes along with the pitch-pitch minimum
 configuration robot.
 Only three electrodes are connected.
 b) The touch strip is placed around one module to form a square 
\begin_inset Quotes eld
\end_inset

touch ring
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\end_inset


\begin_inset CommandInset label
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name "fig:Preliminary-touch-strip"

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\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
The first prototype of touch strip is being made and designed, but a preliminary
 proof of concept has been built.
 It it is shown in figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Preliminary-touch-strip"

\end_inset

a.
 It consist of one layer with 12 electrodes in a flexible PCB, which has
 been taken from a commercial flexible keyboard.
 The strip containing the 12 electrodes has been cut and three wires have
 been soldered for performing preliminary tests.
 The total strip length is 208mm.
 
\end_layout

\begin_layout Standard
In figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Preliminary-touch-strip"

\end_inset

b the strip is placed around one MY1 module, which has a square section.
 As the strip is flexible, it can be fitted to any shape.
 There are three electrodes per side, but only the three at the bottom are
 currently being tested.
 The proof of concept is being done with the pitch-pitch minimum configuration
 robot consisting of two MY1 modules.
 This is the minimum modular robot with locomotion capabilities
\begin_inset CommandInset citation
LatexCommand cite
key "JuanGonzalez-Gomez2008"

\end_inset

.
\end_layout

\begin_layout Section
Experiments
\end_layout

\begin_layout Subsection
Touch strip experiments 
\end_layout

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\align center
\begin_inset Graphics
	filename figures/touch-strip-experiments.eps
	scale 66

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\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Testing the touch strip with the Freescale Sensor Toolbox MPR121 Evaluation
 Kit.
 a) The kit is connected to the standard electrodes supplied by the manufacturer.
 b) Screenshot of the measures taken from the three electrodes of the touch
 strip, using the software provided by Freescale
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name "fig:Testing-the-touch-strip"

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\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
First, we have tested and measured standard capacitive sensors provided
 by the Freescale Sensor Toolbox MPR121 Evaluation Kit shown in figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Testing-the-touch-strip"

\end_inset

a.
 Then we have replaced them by our touch strip prototype to test the viability
 of our idea.
 Even if these preliminary electrodes are not meant for being used as capacitive
 sensors, because the come from a flexible commercial keyboard, they are
 working good enough and the MPR121 chip is able to perform measurements.
 The pressure exerted with the fingers is detected, as shown in fig.
 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Testing-the-touch-strip"

\end_inset

b.
 As can be seen, the idea is working.
 These results are very promising and let us continue to the next step:
 building another touch strip prototype that includes the three layers and
 the 12 electrodes.
\end_layout

\begin_layout Subsection
Modular Grasping simulation
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
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status collapsed

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename figures/snake-grasping.eps
	lyxscale 50
	scale 48

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Simulation of a 30 module snake robot grasping a cylinder.
 a) Simulation in OpenRave.
 b) The contact point cloud obtained from the simulation.
 c) The contact point cloud view from another angle, so that the cylinder
 contour can be seen
\begin_inset CommandInset label
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name "fig:Snake-grasping"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
Some preliminary grasping experiments have been performed in simulation.
 The OpenRave simulator
\begin_inset CommandInset citation
LatexCommand cite
key "openrave"

\end_inset

 has been used along with our OpenMR
\begin_inset Foot
status open

\begin_layout Plain Layout
OpenRave Modular Robots plugin: http://bit.ly/9a3fXk
\end_layout

\end_inset

 plugin for modular robots.
 The testing program obtain the contact points between the snake and the
 cylinder, as well as the applied forces.
 In figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Snake-grasping"

\end_inset

a a 30 module snake robot grasping the cylinder can be seen.
 The contact point cloud is shown in fig.
 
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LatexCommand ref
reference "fig:Snake-grasping"

\end_inset

b.
 When the orientation of these points is aligned with the observer, the
 cylinder contour can be glimpsed.
\end_layout

\begin_layout Section
Conclusions
\end_layout

\begin_layout Standard
We have presented a novel idea for implementing the sense of touch in snake
 modular robots.
 It is based on touch strips placed around the snake section, forming touch
 rings with embedded capacitive sensors.
 Even if this work is in a very preliminary stage of development, the experiment
s carried out confirm the viability of this design.
 In addition, experiments on modular grasping have been simulated for obtaining
 the contact point and forces applied when a snake robot grasp an object.
\end_layout

\begin_layout Standard
Currently we are working in combining the locomotion, climbing and grasping
 capabilities with the sense of touch for the realization of a modular snake
 robot for urban search and rescue operations.
 
\end_layout

\begin_layout Section
Acknowledgments
\end_layout

\begin_layout Standard
This research is partially supported by the HANDLE project, which has received
 funding from the European Community's Seventh Framework Programme (FP7/2007-201
3) under grant agreement ICT 231640.
\end_layout

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bibfiles "myreferences"
options "ieeetr"

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\end_body
\end_document
