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Underwater Robots - Gianluca Antonelli.pdf

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o x<br />

z<br />

o b<br />

z b<br />

x b<br />

3.3 Earth-Fixed-Frame-Based, Non-model-Based Controller 49<br />

f b f b<br />

M r<br />

r b<br />

r b<br />

o b<br />

x b<br />

z b<br />

r g<br />

r g f g<br />

f g<br />

Fig. 3.1. Planar view parallel to the xz earth-fixed frame of two different configurations<br />

and corresponding restoring forces and moments: r G ( r B )isthe center<br />

of gravity (buoyancy), f G ( f B )isthe gravity (buoyancy) force, and M R is the y<br />

component ofthe restoring moment<br />

Reduced Controller. According tothe motivation given in the introduction<br />

of this Section, the following reduced version of the control law isconsidered<br />

g I<br />

τ � v = ˆg �<br />

RB( R I B )+ ˙p r , (3.7)<br />

where ˆg �<br />

RB( R I B )isamodel-based estimate of the restoring generalized force<br />

acting on the vehicle. Itmight beuseful tosubstituting the definition of ˙p r<br />

yielding<br />

τ � v = ˆg �<br />

RB( R I B )+K D ˙˜p d + K P ˜p + K I<br />

that has aclear interpretation.<br />

� t<br />

0<br />

θ<br />

˜p ( τ ) dτ (3.8)<br />

3.3 Earth-Fixed-Frame-Based, Non-model-Based<br />

Controller<br />

In 1999, J.Yuh proposes an earth-fixed-frame-based, non-model-based controller<br />

[320]. The control input is given by:

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