Underwater Robots - Gianluca Antonelli.pdf

114 6. Kinematic Control of UVMSs
similar to the macro-micro manipulator approach [107]; the main difference
is that the latter requires dynamic compensation of the whole system while
the former is based on akinematic control approach. This is advantageous
for underwater applications inwhich uncertainty on dynamic parameters is
experienced.
Simulations
Let consider a9-DOF UVMS constituted by the Naval Postgraduate School
AUV Phoenix [145] with a3-DOF planar manipulator arm. For the sake
of clarity, in this first group of simulations, the attention we was restricted
to planar tasks described in the plane of the manipulator, that is mounted
horizontally. Therefore, let usconsider six degrees of freedom in the system
which ischaracterized bythe three vehicle coordinates x , y , ψ ,and the three
end-effector coordinates x E , y E , ψ E all expressed inaearth-fixed frame; the
three vehicle coordinates z , θ , φ are assumed to be constant. Asketch ofthe
system as seen from the bottom is reported in Figure 6.2, where the earthfixed,
body-fixed, and end-effector reference frames are also shown.
[m]
8
6
4
2
0
− 2
− 4
− 4
− 2
y
b
0
x
b
y
2
[m]
x
4
y x
E E
Fig. 6.2. Sketch ofthe simulated UVMS seen from the bottom
Astation keeping task is considered asfirst case study. During station
keeping, the thrusters must react to the ocean current the strength of which
exhibits aquadratic dependence on the relative velocity [127]. However, if
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