Underwater Robots - Gianluca Antonelli.pdf

176 7. Dynamic Control of UVMSs
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Fig. 7.14. Output feedback control; first case study. Comparison between
the control laws (7.41),(7.42) and (7.62): vehicle control forces. Left: control
law (7.41),(7.42). Right: control law (7.62)
trol structure; also, the control inputs remain free of chattering phenomena
and are not reported for brevity.
The tracking performance obtained with the simplified control law confirms
thatthe controller-observer approachisintrinsicallyrobust with respect
to uncertain knowledge of the system’s dynamics, thanks to the exponential
stability property. Hence, perfect compensation of inertia, Coriolis and centripetal
terms, as well as of hydrodynamic damping terms, is not required.
Third case study. The control laws (7.43),(7.44) and (7.63) have been
tested in more severe operating conditions. Namely, the update rate for the
vehicle position/orientation measurements has been lowered to 5Hzand the
A/D word length has been set to 12 bit for all the sensor output signals.
Gaussian zero-mean noise is still added to the measures. The parameters in
the control laws are the same as in the previous case studies.
Figure 7.18 shows asmall degradation ofthe tracking performance for
both the control schemes. In fact, the tracking errors remain of the same
order of magnitude as in the previous case studies, because the computing
rate of the control law isunchanged (100 Hz). Namely, the update rate of