Underwater Robots - Gianluca Antonelli.pdf

4.5 Experiments 89
Fig. 4.7. Expected and measured motor currents for the vehicle Romeo in case of
flooded thruster (courtesy of M. Caccia, National Research Council-ISSIA)
and does not make use of thruster model neither it needs the vehicle acceleration
as required bythe theory; the block diagram, thus, is simply given by
Figure 4.8. Details on the control law are given in the referenced papers, the
basic formulation ofthe controller is given by:
u v = E † [(¨η d − β )+K v ˙˜η + K p ˜η ] (4.1)
where K v and K v are control gains, the vector ˜η is the position/orientation
error, β represents the compensation of the nonlinear terms of the equation
of motions. The matrix E takes into account the TCM matrix, the inertia
matrix and the Jacobian matrix that converts body-fixed toinertial-fixed
velocities. Generalization about control ofadesired task is given in [233].
The experiments validated the proposed approach; inFigure 4.9 the voltages
are shown: it can be recognized that thrusters 2and 6(one horizontal and
one vertical) are turned off at t =260 sand t =300 s, respectively, this
causes anaugmentation of the chattering of the remaining thrusters that,
however, still can perform the desired task (Figure 4.10).