Underwater Robots - Gianluca Antonelli.pdf

10. Concluding Remarks
“Cheshire-cat —Alice began— would you tell me, please, which way Iought
to go from here?”. “That depends agood deal on where you want to get to”,
said the cheshire-cat.
Lewis Carroll, “Alice’s adventures in wonderland”.
The underwater environment ishostile, the communication is difficult
and external disturbances can strongly affect the dynamics of the system
involved in the mission. Moreover, the sensing devices are not fully reliable
in the underwater environment. This is particularly true for the positioning
sensors. The vehicle actuating systems, usually composed of thrusters, is
highly nonlinear and subject tolimit cycles. Some very simple operations for
aground robotic system, such as to hold its position can become difficult for
UVMSs. This difficulty dramatically increases for complex missions.
Moreover, also ifone wants toneglect the technical difficulties and focus
on the mathematical model he deals with characteristics difficult tohandle.
The equations of motion are coupled and nonlinear; the hydrodynamic effects
are not completely known leading to the practical impossibility toidentify
the dynamic parameters. Together with the complexity ofthe mathematical
model this is aserious obstacle versus the implementation of model-based
control laws.
In this framework, the control of the UVMS must be robust ,inawide
sense, reliable and of simple implementation. With this in mind the techniques
for motion and force control ofUVMSs needs to be developed.
The kinematic control approach is important for accomplishing anautonomous
robotic mission. Differently from industrial robotics, whereanoff-line
trajectory planning is apossible approach, in case of unknown, unstructured
environment, the trajectory has tobebegenerated in real-time. The possible
occurrence of kinematic singularities, thus, is not avoided with a task space
control law. Moreover, UVMSs are usually redundant with respect to the given
task; akinematic control approach, thus, can exploit such aredundancy.
The motion control of UVMSs must deal with the strong constraints discussed
along the book. In this work, different approaches were discussed.
Control ofanunderwater robotic system can not be reduced at the sole
translation of similar approaches designed for ground-fixed manipulator; as
an example,itisinterestingtostress the results achieved in Chapter 3: certain
G. Antonelli: Underwater Robots, 2nd Edition, STAR 2, pp. 237–238, 2006.
© Springer-Verlag Berlin Heidelberg 2006