IEEE Robotics & Automation Magazine - September 2015 - 76

Underwater Diver Interface
The diver carries an underwater interface (a commercially
available tablet) sealed in a custom-made waterproof casing
that has been tested in a pressure chamber for depths up to
50 m. Larger depths can be achieved but at the expense of a
more robust and cumbersome design. The diver-mounted
Bluetooth modem is placed on the waterproof casing, enabling a Bluetooth connection with the tablet without compromising the structural integrity of the casing itself. A tablet
with an inductive touchscreen is integrated in the overall system, allowing the diver to send feedback to the surface platform via an acoustic modem. A commercially available
stencil has been modified to preserve touchscreen functionalities at rated depths. An Android application that has been
developed for this purpose has the following set of
functionalities.
● The diver position transmitted from PlaDyPos is directly
overlayed on an integrated Google map, allowing the diver
absolute localization, as is possible on dry land where a
GPS signal is present.
● Two-way communication with the surface in the form of
predefined or custom short messages is enabled, as well as
a single-touch alert message in case of hazards.
● Waypoints, tracks, or marked areas can be sent from the
surface and displayed directly on the diver's tablet, and
thus the diver can visit areas of interest sent from the
ground station.
A diver carrying the tablet in the underwater casing on dry land
during one of the experiments in Croatia is shown in Figure 4.
Mathematical Modeling
Modeling the ASV
Dynamic Model
Following the notation shown in Figure 5, a dynamic model of
the platform in the horizontal plane can be described using the
velocity vector o = 6u v r@T , where u, v, and r are the surge,
sway, and yaw speed, respectively; and the vector of actuating
forces and moments acting on the platform x = 6X Y N @T ,
where X, Y are the surge
and sway forces and N is
Conducting experiments
the yaw moment [11].
Both vectors are defined
with divers presents
in the body-fixed (mobile)
coordinate frame. The una challenge due to
coupled dynamic model
in the horizontal plane is
uncertainties.
given with (1), where M is
a diagonal matrix with
mass and added mass
terms, and D ^oh is a diagonal matrix consisting of nonlinear
hydrodynamic damping terms
Moo =-D ^oh + x.
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IEEE ROBOTICS & AUTOMATION MAGAZINE

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September 2015

(1)

Figure 4. A diver with the underwater tablet preparing to start
the experiments. The underwater casing, rated for depths up
to 50 m, allows touchscreen functionality when using tablets
with inductive screens. The tablet is linked to the surface via the
acoustic modem mounted on the diving tank.

Since the platform is designed to be symmetrical with respect
to the x and y axes in the body fixed frame, the following
forms of the two matrices are adopted: M = diag ^a u,
a u, a r h, D ^ o h = diag ^ b u ^ u h, b u ^ v h, b r ^ r hh .
Kinematic Model
The kinematic equations for the platform motion in the horizontal plane on the sea surface is given with (2), where x and
y are the position and } is the orientation of the platform in
the Earth-fixed coordinate frame. The rotation matrix R (})
is given with
xo
u
R ^}h 0
> yo H = =0 [1 # 2] 1G>vH
}o
r

(2)

cos } -sin }
E.
R ^}h = ;
sin } cos }

(3)

{E}
yE

xE
zE

ro yB
(Sway) q
(Pitch)

{B}
xB
(Surge)

r (Yaw)

p
(Roll)

zB
(Heave)
Figure 5. The body-fixed and Earth-fixed coordinate frames
attributed to the ASVs. This notation is usually used in marine
vehicles, as described in [11].
Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - September 2015
