Experimental results

Many approaches were implemented and tested for the control system. For instance a linear PI-MIMO (Proportional Integrative - Multiple Input Multiple Output) plus feed-forward structure (Valenciaga et al., 2007) and also a nonlinear fuzzy logic based control were verified in computer simulation. They were applied in a low-cost ocean observing platform, based on a hybrid vehicle between an AUV and autonomous surface vehicle (ASV), called CORMORAN. This robot moves slightly underneath the sea surface following a previously planned route and regularly dives to make vertical profiles of the water column. The PI-MIMO control strategy is used to commands the rudder and the propeller. However, the control system currently mounted in ICTIOBOT is a simple PI-MIMO control in the horizontal plane (2D) minimizing the angle ¡¡, that is given by Equation 1.

where Fis the vehicle's yaw and X the angle given by Equation 2, where (x1,y1) and (x2,y2) the coordinates of the robot and the target waypoint, respectively (figure 6). This is known as the line-of-sight (LOS) guidance law (Naeem et al., 2003). The speed envelope using an ideal particle approach, recently proposed (Breivik and Fossen, 2005) was also tested in computer simulation (Valenciaga et al., 2007), but not yet ported to the prototype.

The navigation system for the preliminary trials showed in this chapter, consisted on a sensor fusion of measures from a compass, an inertial navigation system, a depth sensor and a GPS (when navigating in surface), for self position perception. For pipeline tracking, the prototype used an MBE, to avoid the need of light for image processing near the dark seabed when water is not clear or the applications shift to deeper waters. The knowledge-based DMP was also integrated to the ICTIOBOT prototype. The evolutionary robotic OAS was not ready to be tested in these trials. Several tests were carried out in the sea surface and slightly underneath the surface, to have available the signal from GPS in all the cases.

These modules were tested in the trials done in Cala Estancia that is bay with scanty meters of depth, near to Palma de Mallorca, Spain, in April 2008. A curved trajectory was the reference of the step points, represented by solid red line in figure 7, whereas the punctuated line in the same figure represents the real position described by the AUV.

P target

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